My brother's kid has recently been being really bad. Before I get into this, I just want to point out the fact that my brother is an EXCELLENT father, he's 24 years old and has had plenty of experience in helping raise our younger siblings. Him and his wife have their own house and everything, so that shouldn't be an issue. The kid, 4 years old, breaks stuff, hits other kids, doesn't listen, won't sit still, etc. Here's a couple examples of what the kid has done. The other day he sprayed a baby in the face with carpet cleaner and the baby's mom had to take him to the emergency room. Today, he punched his mom in the face!
My brother has tried many combinations of punishments, spanking, yelling, the "dad" stare, guilt trips, even positive reinforcement. This kid is different though. He's sneaky. Instead of him learning a lesson from getting punished, he will just find other ways to accomplish his goals. We don't know if he is doing it just because he wants to, or if he is doing it BECAUSE he knows it's bad. For the most part, he's good around my brother but as soon as he leaves, he has the urge to do bad.
Is there something my brother should be doing, or not doing?
*EDIT* He does plan to take the kid to a professional but I wanted to ask you guys for any advice I could give him.