I'm buying my son a helmet lol this little boy has started hitting his head on the wall when he's…

I'm buying my son a helmet lol this little boy has started hitting his head on the wall when he's sleepy and he does it really hard too. I tell him to stop and no but he thinks it's funny. I think it has to do with his dad though because Joey hits himself or let's him throw stuff at him because Andrew finds it funny.