These are not just baby behaviors. All birds (not just 'tiels) yawn/neck stretch to adjust their crop. It is a normal part of bird anatomy and behavior. As far as flock-calling, that is typical cockatiel behavior in general and has nothing to do with weaning. The baby begging behavior is a different type of call/motion.Yes, he is clearing out his crop as the last person explained. How old is he? It sounds like he is having typical "baby" behavior while adjusting to his new home. If he was not properly weaned when you got him, he will cry a lot too.