I am fully aware of how
protected abstract ContentValues getSaveData ()
So, is there any way to mimic a children-only modifier in Java?
Nope. The only access modifiers we've got are the ones you listed. There's also "default" visibility, aka "package-private", but that does not make elements accessible to subclasses. So you could probably just use
protected and not worry about it.
It sounds like a better solution might be a refactor of your code, but there's not much concrete in your question to go on.