Flutter table structure

I would suggest using the Table Widget for consistency and ease as nested rows and columns can get a little messy and far indented.

https://docs.flutter.io/flutter/widgets/Table-class.html

   ...
Table(children: [
  TableRow(children: [
    Text("item 1"),
    Text("item 2"),
  ]),
  TableRow(children:[
    Text("item 3"),
    Text("item 4"),
  ]),
]);

using flex(by default it's 1) you can separate the two columns and then use the crossAxisAlignmentto align them items in the beginning :

  new Container(
    decoration: new BoxDecoration(color: Colors.grey),
    child: new Row(
      children: <Widget>[
        Expanded(
          child: new Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              new Container(
                decoration: new BoxDecoration(color: Colors.red),
                child: new Text("item 1"),
              ),
              new Container(
                decoration: new BoxDecoration(color: Colors.amber),
                child: new Text("item 3"),
              ),
            ],
          ),
        ),
        Expanded(
          child: new Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              new Container(
                decoration: new BoxDecoration(color: Colors.green),
                child: new Text("item 2"),
              ),
              new Container(
                decoration: new BoxDecoration(color: Colors.teal),
                child: new Text("item 4"),
              )
            ],
          ),
        )
      ],
    ),
  )