Does the boy's mother step in if she's there to stop the hitting? If she's there but isn't doing anything, feel free to step in yourself and say something to the effect of "We don't hit in this house, you'll have to go home if you can't play nicely"
It's also ok for your daughter to take a break from playing with him too. His behaviour is typical two year old behaviour (not that it makes it right) but some time apart might not hurt. Not forever. Just maybe one week you don't get the kids together.
Try catching them doing good. When they're together and playing well, compliment them on it. Be specific. Reinforcing positive behaviour is a lot easier and goes a lot further (not to mention reduces the need to discipline).
at 1:34 PM on Dec. 12, 2008