How do you know he sits on his own? Does he tell you that nobody plays with him or have you seen him/been told by someone? The reason I ask is because my DS1 told me that no one plays with him at lunch time too, yet when I dropped him off/picked him up he would always play with kids. He is such a social creature and I was quite worried so I spoke to his teacher. She wasn't worried at all and we worked out that DS1's idea of "nobody plays with me" meant "they won't play my game". Apparently it's quite common at this age for boys to not have close friendships (compared to girls) and they tend to play alone a lot.

My friend's DD who is the same age complained of the same thing and we worked out she was the same as DS1, no one wanted to play her games LOL!

The kids have all started playing tiggy at school and DS1 spends every play time joining in because it's his kind of game, I haven't had him complain of no one to play with since. Maybe your DS should initiate a game of tiggy!

Could you ask his teacher to pair him up with someone? DS1 was asked to hang out with a new boy in his class recently and they have become great friends.

I'm sure he'll settle in soon, I get the feeling he has a gorgeous personality