Wrap

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyPage(),
    );
  }
}

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Container(
      child: Padding(
        padding: EdgeInsets.only(top: 100),
        child: Wrap(
          spacing: 10,
          runSpacing: 10,
          direction: Axis.horizontal,
          children: <Widget>[
            FlatButton(
              color: Colors.red,
              child: Text("Button"),
              onPressed: () {},
            ),
            FlatButton(
              color: Colors.red,
              child: Text("Button"),
              onPressed: () {},
            ),
            FlatButton(
              color: Colors.red,
              child: Text("Button"),
              onPressed: () {},
            ),
            FlatButton(
              color: Colors.red,
              child: Text("Button"),
              onPressed: () {},
            ),
          ],
        ),
      ),
    ));
  }
}