Flutter container inside a container

You need to specify where in the orange box you would like the blue box displayed, otherwise the blue box will grow to the size of its parent.

  Container(
    width: 200.0,
    height: 200.0,
    color: Colors.orange,
    alignment: Alignment.center, // where to position the child
    child: Container(
      width: 50.0,
      height: 50.0,
      color: Colors.blue,
    ),
  ),