I'm sure that all of what you says applies to some degree (lower IQ, less punishment, etc), but it really comes down to biological development. Child brains simply aren't developed enough to (a) remember past behavior correctly, (b) connect behavior to punishment, (c) calculate risks. So when a child has a desire, they simply don't have the biological capacity to think about consequences very well.
I'd also add that maybe children become socialized well by misbehaving. It's a weird idea, but it's a common observation that children are always "pushing the boundary." For example, children will test the "keep your hands to yourself" rule by moving their finger very close to your face and say "I'm not touching you!" Although it's annoying, this behavior will teach kids (via punishment) that people don't want to be touched and they need some personal space as well. Without the misbehavior, they never really learn the improtance of personal space. I'm sure that much of the unspoken rules of personal interaction are learned in this fashion (misbehavior-punishment cycles). Fabio