How to pass different objects to gwt?

Question

Java

Hello dear gurus.
I can not deal with the collection in GWT
The task is this, you need to get all the children of the object.
Problem: Children can be of different object types, but all inherit from the same ObjectBD
Current implementation:
Sending a GET request with RestyGWT, it returns a List<? super ObjectBD> in JSON format
But the interface in GWT cannot use wildCard. And I get all the objects truncated to the same type and I can’t cast by a unique attribute either, a cast error occurs due to the fact that there are not enough variables to pass to the constructor (they were truncated when casting in ObjectBD).
Question: How to be? use a different transfer format?