Why are most of the adults such Jerkasses or idiots in these shows? Because odds are they shared the same kind of childhood where they where badly infulenced by adults like that. Overlaps with Fridge Horror if you think about it; odds are our favorite characters might grow up to be no better.
Robbie denies Rex is a puppet, and there are times where Rex makes noises on his own. And in a recent Sam & Cat episode, a doll they where supposed to babysit turns out to be alive. Lets just leave it at that.