I need a mindmap on latex that have children that begot children

As for your point:

1. If you want A1 to have children, you need to put them in the curly braces after A1, not A2.
2. You can set a growing angle explicitly with grow=<angle>.
3. The level distances, which determine the distances of the children from their parents were already set in your code with keys like level 1/.append style={level distance=8.2cm,...},. You shrink the frame, I do not know why. In any case, you need to adjust the distances to take into account the shrining factor.
4. The children of B2 can be set in the same way as the children of A1. This point has also been addressed in koleygr's answer.

Other than that I find your preamble a bit extensive. I am wondering if you need all of this.

\documentclass[handout,14pt]{beamer}


\usepackage{pgfpages}
\pgfpagesuselayout{2 on 1}[a4paper]

\usetheme{Madrid}
\useoutertheme{miniframes} % Alternatively: miniframes, infolines, split
\useinnertheme{circles}
\makeatletter
\def\beamer@writeslidentry{\clearpage\beamer@notesactions}
\makeatother

\definecolor{navyblue}{rgb}{0.36, 0.57, 0.9} % Navy Blue (primary)
\definecolor{gold(metalic)}{rgb}{0.53, 0.0, 0.69} % Gold(metalic) (secondary)
\definecolor{guppiegreen}{rgb}{0.0, 1.0, 0.0}% (tertiary)

\definecolor{black}{rgb}{0.17, 0.09, 0.03}% (tertiary1)

\definecolor{white}{rgb}{1.0, 1.0, 1.0}% (tertiary2)

\setbeamercolor{palette primary}{bg=navyblue,fg=black}
\setbeamercolor{palette secondary}{bg=navyblue,fg=black}
\setbeamercolor{palette tertiary}{bg=gold(metalic),fg=white}
\setbeamercolor{palette quaternary}{bg=navyblue (metalic),fg=white}
\setbeamercolor{structure}{fg=navyblue} % itemize, enumerate, etc
\setbeamercolor{section in toc}{fg=navyblue} % TOC sections

\usepackage{textpos}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{listings}
\usepackage{amssymb} 
\usepackage{amsmath}
\usepackage{array}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric,arrows}
\usepackage{graphicx}


%%%%%%%%%%%%%%                  %%%%%%%%%%%%%%

\newif\ifsidebartheme
\sidebarthemetrue

\newdimen\contentheight
\newdimen\contentwidth
\newdimen\contentleft
\newdimen\contentbottom
\makeatletter
\newcommand*{\calculatespace}{%
\contentheight=\paperheight%
\ifx\beamer@frametitle\@empty%
\setbox\@tempboxa=\box\voidb@x%
\else%
\setbox\@tempboxa=\vbox{%
\vbox{}%
{\parskip0pt\usebeamertemplate***{frametitle}}%
}%
\ifsidebartheme%
\advance\contentheight by-1em%
\fi%
\fi%
\advance\contentheight by-\ht\@tempboxa%
\advance\contentheight by-\dp\@tempboxa%
\advance\contentheight by-\beamer@frametopskip%
\ifbeamer@plainframe%
\contentbottom=0pt%
\else%
\advance\contentheight by-\headheight%
\advance\contentheight by\headdp%
\advance\contentheight by-\footheight%
\advance\contentheight by4pt%
\contentbottom=\footheight%
\advance\contentbottom by-4pt%
\fi%
\contentwidth=\paperwidth%
\ifbeamer@plainframe%
    \contentleft=0pt%
\else%
\advance\contentwidth by-\beamer@rightsidebar%
\advance\contentwidth by-\beamer@leftsidebar\relax%
\contentleft=\beamer@leftsidebar%
\fi%
}
\makeatother

\setbeamertemplate{caption}[numbered]%put number on figure and table

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{caption}
\usepackage{subcaption}
\captionsetup{compatibility=false}
\makeatletter
\let\orig@subref\subref

\renewcommand{\subref}{%
\@ifstar{\subref@starred}{\subref@unstarred}%
}

\newcommand{\subref@starred}[1]{%
\orig@subref*{#1}%
}

\newcommand{\subref@unstarred}[1]{%
\hyperlink{#1}{\orig@subref*{#1}}%
}
\makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% for fancy box
\usepackage{fancybox}
\usepackage{ragged2e}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%for spotlight highliting
\usepackage{spot} 
\RequirePackage{tikz}
\usetikzlibrary{shapes}
\usetikzlibrary{fadings}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usetikzlibrary{mindmap,trees,shadows}
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\setbeamercolor{emph}{fg=blue}
\renewcommand<>{\emph}[1]{%
{\usebeamercolor[fg]{emph}\only#2{\itshape}#1}%
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%for arc and angles
\usetikzlibrary{calc, angles}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\RequirePackage{luatex85}
\usepackage{luamplib}

\usepackage[round]{natbib} 



\title{Working Title: }
\institute[LATEXD]{A  SEMINAR PRESENTED IN DEPARTMENT OF latex}
\date{\today}

\usepackage{mathptmx}% http://ctan.org/pkg/mathptmx% is TIME NEW ROMANS
\usepackage{tgtermes} % times font
%\usepackage{wordlike}% Emulate MS Word

\usepackage{changepage,mathtools,amsthm,tikz,blindtext}
\usepackage{inputenc,float,caption,subcaption,enumitem}
\usepackage[font=large,labelfont=bf,font=bf,labelsep=space]{caption}
\usepackage[font=small,labelfont=bf,font=bf,labelsep=space]{subcaption}



\usepackage{datetime}

\newdateformat{monthyeardate}{%
\monthname[\THEMONTH], \THEYEAR}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%for arc and angles
\usetikzlibrary{calc, angles}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\RequirePackage{luatex85}
\usepackage{luamplib}
\usetikzlibrary{mindmap}
    \begin{document}
    \begin{frame}[fragile, shrink=72]
    \frametitle{~}
    \begin{block}{Time Series Broad Classification}
        \begin{figure}%[H]
            \centering
            \begin{tikzpicture}
        [decoration={start radius=1cm, end radius=.5cm,amplitude=3mm,angle=30}]

        % Define experience colors
        \colorlet{afcolor}{blue!50}
        \colorlet{mdcolor}{red!75}
        \colorlet{nmndcolor}{orange!80}
        \colorlet{nmescolor}{teal!70!green}
        \colorlet{citscolor}{violet!75}

        \begin{scope}[mindmap,
        every node/.style={concept, circular drop shadow, minimum size=0pt,execute at begin node=\hskip0pt, font=\bfseries},
        root concept/.append style={
            concept color=black, fill=white, line width=1.5ex, text=black, font=\huge\scshape\bfseries,},
        level 1 concept/.append style={font=\bfseries},
        text=white,
        partner/.style={concept color=blue!80!black},
        air force/.style={concept color=afcolor},
        metadata/.style={concept color=mdcolor},
        nmnd/.style={concept color=nmndcolor},
        nmes/.style={concept color=nmescolor},
        cits/.style={concept color=citscolor},
        grow cyclic,
        level 1/.append style={level distance=6cm},
        level 2/.append style={level distance=5cm,font=\small},
        level 3/.append style={level distance=4cm}]
        \node [root concept] (team) {A }%[%rotate=20.5] % root


        child [partner,grow=20] { node {A1}
            child [air force,grow=-40] { node {B3} }
            child [nmnd,grow=20] { node {B2} 
              child [cits,grow=-70]{ node {C1} }
              child [cits,grow=-10]{ node {C2} }
              child [cits,grow=50]{ node {C3} }
            }
            child [nmes,grow=80] { node {\textbf{B1}} }
        }
        child [partner,grow=70] { node {A2}
        };
        \end{scope}

        \begin{scope}[xshift=-4.5cm, yshift=-6cm,every node/.style={align=left,text=black}]
        \matrix[row sep=0pt,column sep=1mm, align=left, nodes={align=left, anchor=west}] {
            \fill [afcolor] (0,.25ex) circle (1ex); & \node{A};\\
            \fill [mdcolor] (0,.25ex) circle (1ex); & \node{A};\\
            \fill [nmndcolor] (0,.25ex) circle (1ex); & \node{A Environment};\\
            \fill [nmescolor] (0,.25ex) circle (1ex); & \node{A};\\
            \fill [citscolor] (0,.25ex) circle (1ex); & \node{A};\\
        };
        \end{scope}
        \end{tikzpicture}
        \caption{Broad Classification of ALPHABET}
        \label{fig3.1a}
    \end{figure}
\end{block}
\end{frame}
\end{document}

Something like this?

\documentclass[handout,14pt]{beamer}


\usepackage{pgfpages}
\pgfpagesuselayout{2 on 1}[a4paper]

\usetheme{Madrid}
\useoutertheme{miniframes} % Alternatively: miniframes, infolines, split
\useinnertheme{circles}
\makeatletter
\def\beamer@writeslidentry{\clearpage\beamer@notesactions}
\makeatother

\definecolor{navyblue}{rgb}{0.36, 0.57, 0.9} % Navy Blue (primary)
\definecolor{gold(metalic)}{rgb}{0.53, 0.0, 0.69} % Gold(metalic) (secondary)
\definecolor{guppiegreen}{rgb}{0.0, 1.0, 0.0}% (tertiary)

\definecolor{black}{rgb}{0.17, 0.09, 0.03}% (tertiary1)

\definecolor{white}{rgb}{1.0, 1.0, 1.0}% (tertiary2)

\setbeamercolor{palette primary}{bg=navyblue,fg=black}
\setbeamercolor{palette secondary}{bg=navyblue,fg=black}
\setbeamercolor{palette tertiary}{bg=gold(metalic),fg=white}
\setbeamercolor{palette quaternary}{bg=navyblue (metalic),fg=white}
\setbeamercolor{structure}{fg=navyblue} % itemize, enumerate, etc
\setbeamercolor{section in toc}{fg=navyblue} % TOC sections

\usepackage{textpos}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{listings}
\usepackage{amssymb} 
\usepackage{amsmath}
\usepackage{array}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric,arrows}
\usepackage{graphicx}


%%%%%%%%%%%%%%                  %%%%%%%%%%%%%%

\newif\ifsidebartheme
\sidebarthemetrue

\newdimen\contentheight
\newdimen\contentwidth
\newdimen\contentleft
\newdimen\contentbottom
\makeatletter
\newcommand*{\calculatespace}{%
\contentheight=\paperheight%
\ifx\beamer@frametitle\@empty%
\setbox\@tempboxa=\box\voidb@x%
\else%
\setbox\@tempboxa=\vbox{%
\vbox{}%
{\parskip0pt\usebeamertemplate***{frametitle}}%
}%
\ifsidebartheme%
\advance\contentheight by-1em%
\fi%
\fi%
\advance\contentheight by-\ht\@tempboxa%
\advance\contentheight by-\dp\@tempboxa%
\advance\contentheight by-\beamer@frametopskip%
\ifbeamer@plainframe%
\contentbottom=0pt%
\else%
\advance\contentheight by-\headheight%
\advance\contentheight by\headdp%
\advance\contentheight by-\footheight%
\advance\contentheight by4pt%
\contentbottom=\footheight%
\advance\contentbottom by-4pt%
\fi%
\contentwidth=\paperwidth%
\ifbeamer@plainframe%
    \contentleft=0pt%
\else%
\advance\contentwidth by-\beamer@rightsidebar%
\advance\contentwidth by-\beamer@leftsidebar\relax%
\contentleft=\beamer@leftsidebar%
\fi%
}
\makeatother

\setbeamertemplate{caption}[numbered]%put number on figure and table

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{caption}
\usepackage{subcaption}
\captionsetup{compatibility=false}
\makeatletter
\let\orig@subref\subref

\renewcommand{\subref}{%
\@ifstar{\subref@starred}{\subref@unstarred}%
}

\newcommand{\subref@starred}[1]{%
\orig@subref*{#1}%
}

\newcommand{\subref@unstarred}[1]{%
\hyperlink{#1}{\orig@subref*{#1}}%
}
\makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% for fancy box
\usepackage{fancybox}
\usepackage{ragged2e}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%for spotlight highliting
\usepackage{spot} 
\RequirePackage{tikz}
\usetikzlibrary{shapes}
\usetikzlibrary{fadings}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usetikzlibrary{mindmap,trees,shadows}
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\setbeamercolor{emph}{fg=blue}
\renewcommand<>{\emph}[1]{%
{\usebeamercolor[fg]{emph}\only#2{\itshape}#1}%
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%for arc and angles
\usetikzlibrary{calc, angles}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\RequirePackage{luatex85}
\usepackage{luamplib}

\usepackage[round]{natbib} 



\title{Working Title: }
\institute[LATEXD]{A  SEMINAR PRESENTED IN DEPARTMENT OF latex}
\date{\today}

\usepackage{mathptmx}% http://ctan.org/pkg/mathptmx% is TIME NEW ROMANS
\usepackage{tgtermes} % times font
%\usepackage{wordlike}% Emulate MS Word

\usepackage{changepage,mathtools,amsthm,tikz,blindtext}
\usepackage{inputenc,float,caption,subcaption,enumitem}
\usepackage[font=large,labelfont=bf,font=bf,labelsep=space]{caption}
\usepackage[font=small,labelfont=bf,font=bf,labelsep=space]{subcaption}



\usepackage{datetime}

\newdateformat{monthyeardate}{%
\monthname[\THEMONTH], \THEYEAR}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%for arc and angles
\usetikzlibrary{calc, angles}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\RequirePackage{luatex85}
\usepackage{luamplib}
\usetikzlibrary{mindmap}
    \begin{document}
    \begin{frame}[fragile, shrink=72]
    \frametitle{~}
    \begin{block}{Time Series Broad Classification}
        \begin{figure}%[H]
            \centering
            \begin{tikzpicture}
        [decoration={start radius=1cm, end radius=.5cm,amplitude=3mm,angle=30}]

        % Define experience colors
        \colorlet{afcolor}{blue!50}
        \colorlet{mdcolor}{red!75}
        \colorlet{nmndcolor}{orange!80}
        \colorlet{nmescolor}{teal!70!green}
        \colorlet{citscolor}{violet!75}

        \begin{scope}[mindmap,
        every node/.style={concept, circular drop shadow, minimum size=0pt,execute at begin node=\hskip0pt, font=\bfseries},
        root concept/.append style={
            concept color=black, fill=white, line width=1.5ex, text=black, font=\huge\scshape\bfseries,},
        level 1 concept/.append style={font=\bfseries},
        text=white,
        partner/.style={concept color=blue!80!black},
        air force/.style={concept color=afcolor},
        metadata/.style={concept color=mdcolor},
        nmnd/.style={concept color=nmndcolor},
        nmes/.style={concept color=nmescolor},
        cits/.style={concept color=citscolor},
        grow cyclic,
        level 1/.append style={level distance=8.2cm,sibling angle=-60},
        level 2/.append style={level distance=6cm,sibling angle=60}],
        level 3/.append style={level distance=6cm,sibling angle=60}]
        \node [root concept] (team) {A }[rotate=20.5] % root


        child [partner] { node {A1}
        }
        child [partner] { node {A2}
            child [air force] { node {\small B3} }
            child [nmnd] { node {\small B2} child {node {\footnotesize C1}} child {node {\footnotesize C2}} child {node {\footnotesize C3}}}
            child [nmes] { node {\small \textbf{B1}} }
        };
        \end{scope}

        \begin{scope}[xshift=-4.5cm, yshift=-12.5cm,every node/.style={align=left,text=black}]
        \matrix[row sep=0pt,column sep=1mm, align=left, nodes={align=left, anchor=west}] {
            \fill [afcolor] (0,.25ex) circle (1ex); & \node{A};\\
            \fill [mdcolor] (0,.25ex) circle (1ex); & \node{A};\\
            \fill [nmndcolor] (0,.25ex) circle (1ex); & \node{A Environment};\\
            \fill [nmescolor] (0,.25ex) circle (1ex); & \node{A};\\
            \fill [citscolor] (0,.25ex) circle (1ex); & \node{A};\\
        };
        \end{scope}
        \end{tikzpicture}
        \caption{Broad Classification of ALPHABET}
        \label{fig3.1a}
    \end{figure}
\end{block}
\end{frame}
\end{document}

PS: I just added the childs ... but can't know if this is enough because my addition does not add something in the knowledge already needed for your MWE...