Reload child component when variables on parent component changes. Angular2

On Angular to update a component including its template, there is a straight forward solution to this, having an @Input property on your ChildComponent and add to your @Component decorator changeDetection: ChangeDetectionStrategy.OnPush as follows:

import { ChangeDetectionStrategy } from '@angular/core';

@Component({
    selector: 'master',
    templateUrl: templateUrl,
    styleUrls:[styleUrl1],
    changeDetection: ChangeDetectionStrategy.OnPush    
})

export class ChildComponent{
  @Input() data: MyData;
}

This will do all the work of check if Input data have changed and re-render the component

update of @Vladimir Tolstikov's answer

Create a Child Component that use ngOnChanges.

ChildComponent.ts::

import { Component, OnChanges, Input } from '@angular/core';
import { ActivatedRoute } from '@angular/router';

@Component({
  selector: 'child',
  templateUrl: 'child.component.html',
})

export class ChildComponent implements OnChanges {
  @Input() child_id;

  constructor(private route: ActivatedRoute) { }

  ngOnChanges() {
    // create header using child_id
    console.log(this.child_id);
  }
}

now use it in MasterComponent's template and pass data to ChildComponent like:

<child [child_id]="child_id"></child>

In case, when we have no control over child component, like a 3rd party library component.

We can use *ngIf and setTimeout to reset the child component from parent without making any change in child component.

.template:

<child-component *ngIf="show"></child-component>
<button (click)="resetChildForm()"></button>

.ts:

show:boolean = true

resetChildForm(){
   this.show = false;

   setTimeout(() => {
      this.show = true
    }, 100);
}

Use @Input to pass your data to child components and then use ngOnChanges (https://angular.io/api/core/OnChanges) to see if that @Input changed on the fly.