MainAxisAlignment

CrossAxisAlignment

Column(
  mainAxisAlignment: MainAxisAlignment.center,
  mainAxisSize: MainAxisSize.max,
  crossAxisAlignment: CrossAxisAlignment.center,
  children: [
    Container(
      padding: const EdgeInsets.all(0.0),
      color: Colors.cyanAccent,
      width: 80.0,
      height: 80.0,
    ),
    Container(
      padding: const EdgeInsets.all(0.0),
      color: Colors.blueAccent,
      width: 80.0,
      height: 80.0,
    ),
    Container(
      padding: const EdgeInsets.all(0.0),
      color: Colors.orangeAccent,
      width: 80.0,
      height: 80.0,
    ),
  ],

Reference:
http://flutterexamples.com/