Two and a half is very young i would not worry to much at this stage a school is a big place for a toddler.He is only a baby yet he will be fine in a year or so when he is a bit older.My daughter was the same when she was that age i thought it would be good for her to mix with other children because she was a only child but she hated it the health vistor advised me not to send her if she did not like it as she is probley not quite ready.She is now 5 and she loves school and has lots of friends try not to worry.