I like M2FM's post and mine would have been very similar. I just want to add that you have to get the parents to do what you are doing at home or forget it.

Hugging is always nice but I have a 2 year old boy who didn't understand anything let alone personal space until a couple months ago and I know how frustrated the other children will get when they are busy and another child invades their space with no empathy for their feelings. Every child deserves to be able to play without having another child ploughing through! I hear ya but I think repeating yourself until you're blue in the face is really your only option. Use a really stern voice and hopefully he'll get it soon.