I'm pretty strict with hitting. No chances instant consequence. If we're out he is removed from the situation for a specific amount of time and if its at home straight to his room. He is getting better, but he only ever hit his sister and it was usually because he thought it was funny. This past week he's been pretty good so I think its actually sinking in. We also do as Elli suggested and have a big chat about it, if we ask him what he did he do he will say "Hit Sissy. No Seth. No hit Sissy. Sorry Mummy." So he does get it, then he has to apologise to the person he has hit and we kinda remind him of it over the next few hours and praise him for playing nicely and tell him he's being a good boy. Luckily he's not done it to anyone outside of home but regardless he still needs to know its not ok.

I'm really funny about physical disrespect so its one thing I like to really nip in the bud.