20 month old hitting out-any advice?

[sureitsgrand]

My 20 month old usually goes to a creche two days a week and is with his grandparents the other two days, I work a four day week. My parents have been unable to take him for the last fortnight due to health reasons, so he temporarily was doing 4 days in creche. Since this started, I have been informed by staff he has started hitting the other children. The staff said when they ask him to stop, say No, or remove him from the situation he just laughs and is also laughing when he does it. He's done it a few times at home here too, he has hit me and the dog. If I explain it's not nice, or say nice hands etc he just laughs or repeats it.
I have taken some time off so he no longer has to spend 4 days in creche, until my parents can take him again, I think he's either over stimulated with all the changes, or its a phase?! Any ideas? Thank you.

[Bubspub]

I don't have any answers I'm afraid but posted a similar thread today (17mo kicking/swiping when people come into his space) so I'll be watching this too see if anyone has any useful advice I think this board is quite quiet x