This class is completely pointless in python. It provides no added functionality, and there is only one class that subclasses it so it's not like it's being used in an instanceof check. If it's needed in the future it is trivial to extract it out at the time a ChildNode class was created, assuming at that time there is some sort of common functionality.

I could see it's need in Java since we may want a statically typed list of all nodes, but in python it looks really out of place.