DS (3.2) is generally a lovely little boy, he has nice manners and my friends often comment on how calm he is and how he gets on and plays nicely.
However, apart from the friends that he does like, he is very 'funny' with other children. He doesn't seem to like anyone younger (apart from his new born sister). When is sees other children out and about, he hisses and makes faces at them and shouts NO! at them for no reason at all. He gets on very well with his friends but yesterday we took him to see his new nursery and he didn't like it when a boy came over to the garage that he was playing with and sat there. He hissed and made faces until the boy went away. Then after he threw a car at him (I was mortified), but later when a girl came over to play, he was fine with that and told me this morning that he liked her (it isn't specific to girls or boys either, just certain children).
We have been going to groups since he was 5 months as I wanted him to be ok with being around other children as I am a SAHM and he was an only child until 8 weeks ago. He has also had one creche session of 3 hours a week from the age of 1 so he would be ok with being left somewhere without me there all the time and so he could socialise, I know there are a couple of boys there he is friends with as he mentions them often.
Why is he doing this and what can I do? I am getting really embarrassed when other parents must think I have a really rude child on my hands but generally he just isn't like this.