type 'List<dynamic>' is not a subtype of type 'List<Widget>'

The problem here is that type inference fails in an unexpected way. The solution is to provide a type argument to the map method.

snapshot.data.documents.map<Widget>((document) {
  return new ListTile(
    title: new Text(document['name']),
    subtitle: new Text("Class"),
  );
}).toList()

The more complicated answer is that while the type of children is List<Widget>, that information doesn't flow back towards the map invocation. This might be because map is followed by toList and because there is no way to type annotate the return of a closure.

You can Cast dynamic List to List With specific Type:

List<'YourModel'>.from(_list.where((i) => i.flag == true));

I have solve my problem by converting Map to Widget

      children: snapshot.map<Widget>((data) => 
               _buildListItem(context, data)).toList(),