He is only 4 (not even 4 and a half yet!!).
He bit one of his best friends and I know that it is completely unacceptable and needed punishing but his teacher told me she had never seen a child so distraught when he was being told off by the headteacher....and I just wanted to give him a big cuddle as he is still so young and my baby 
He has never bitten anyone before so it is completely out of the blue (even the teacher admitted this)
He wouldn't talk about it last night - just kept saying 'don't know' or 'can't remember' so I don't know how much of what went on yesterday sunk in!
Any advice on how to handle it - I am dreading picking him up at the moment as this is the second time in 3 days the teacher has had to speak to us about his behaviour (the first time was an accumalation of silly minor behaviour which he is going through a phase of at the moment).
What do we need to do at home to correct his behaviour??