class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocProvider<BlocA>(
      builder: (BuildContext context) => BlocA(),
      child: BlocProvider<BlocB>(
        builder: (BuildContext context) => BlocB(),
        child: BlocProvider<BlocC>(
          builder: (BuildContext context) => BlocC(),
          child: ChildA(),
        )
      ),
    );
  }
}