So far whenever I needed to use a conditional statement within a Widget I have done the following (Using Center and Containers as simplified dummy examples):
For the record, Dart 2.3 added the ability to use if/else statements in Collection literals. This is now done the following way:
return Column(children: [ Text("hello"), if (condition) Text("should not render if false"), Text("world") ],);
Flutter Issue #28181 - Inline conditional rendering in list