If he's talked to you and told you he is coming, by all means go sit with him. They often like to find out what kind of people his parents are. Make sure your son runs over to greet him before the game and talks to him afterwards.
Just tell him, to feel free to go off on his own and do his thing, you all won't be offended at all if he wants to be by himself. Buy him a coke, be a good host. Don't brag about your boy, just answer questions he asks about them. Don't go on and on. Talk up other players on the team that are good though. Don't tear anyone down.