Should I be worried by 21 Month old hitting himself?

[MammaTo2boys]

This is not a debate on whether smacking your child is right or wrong, however, DH and I have chosen not to use that form of punishment/reprimand for our DS1. So having never hit him, or shown him any other similar kind of behaviour, he is now coming home from Nursery and hitting/tapping his own hand and saying naughty. He does this when he has thrown something or doesn't do as he is told, so it is like he is telling himself off before me or DH does. But as I say this has me baffled as we don't hit or smack him. Could this just be a phase he is going through or is it learned behaviour? I am worried that someone is hitting him at nursery, but I don't want to go in all guns blazing have misread the signals.
All advice gratefully received.

Hi don't know if this is a phase for your child or not but thought I would reply as my DS did this from the age of about 4yr and for similar reasons, it seems like he is trying to punish himself. He is 6yrs old now and occasionally still does it. I find it really distressing to watch and like you we've never used smacking to discipline so I've no idea where it comes from. I ask him not to do it and to talk to me if he's upset/angry about something.

The only other child I know who does this is a boy in DS class. I asked the mum about it and she says it's like her son just wants to punish himself and takes out any frustration on himself.

Sorry I've propably not been much help but just to know you're not on your own and I'd be interested to hear any more views about it.

Thanks Sj99, for your thoughts, it's heartbreaking isn't it. DS1 is a really well behaved little boy and I don't want him thinking that he is naughty all the time and I don't like the possibility that somebody could be repremanding him in a manner that I don't think is appropriate. I just hope I am over reacting and that it is not that sinister.
Thanls once again for your time.