Вы можете добавить SizedBox
между детьми.
SizedBox(
width: 200.0,
height: 300.0,
)
Ваш код может быть отредактирован в
Container(
margin: new EdgeInsets.all(2.0),
color: Colors.red,
padding: EdgeInsets.all(10.0),
child: GridView.count(
physics: NeverScrollableScrollPhysics(),
shrinkWrap: true,
crossAxisCount: 6,
children: <Widget>[
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
SizedBox(width: 10,height: 10,),
Image.asset('images/user.png', width: 30.0),
],
),
),