My son asks me to him and i think its not ok am i right?

My son is 7 years old and he was started to ask me to me as a punishment. When he was younger we never ed him or our other kids. He tries to do things so he can get ed like pulling his sisters hair and writing on the walls and swearing and stuff like that. I don't know what to do sometimes is im bending over to get something he smacks my bottom. And last week his sister took his toy and he got her and pulled her over his knee and ed her. I was so shocked to see that. He also plays with his sisters baby dolls and he pretends they misbehave and he s then and he takes of their panties as well. Im worried about this and i don't know what to do. can anyone help me?