Naive example for Expanding Child inside ExpansionTile

main.dart

import 'package:flutter/material.dart';

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

final kExpansionTileHeight = 114;

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.start,
          children: <Widget>[
            ExpansionTile(
              title: Text('Expand me'),
              children: [
                SizedBox(
                  height:
                      MediaQuery.of(context).size.height - kExpansionTileHeight,
                  child: IntrinsicHeight(
                    child: Container(
                      alignment: Alignment.center,
                      color: Colors.blue.shade500,
                      child: Text("I'm expanded!"),
                    ),
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}