thanks for the advice. I think you're right, they are testing boundaries and wanting a reaction so perhaps the ignoring technique would be better.
We had the day from hell on Saturday! I've never seen a child be so naughty! (I haven't been around that many kids so perhaps a slight exaggeration). We had a BBQ with Emma, Maya and the Gremlins and Caitlin even pushed them around and smacked them!

They've all been buddies for ages!!! I was so angry and embarrased