K.
I agree with all the advice here with just one added thought... It might have been jealousy over the little one getting attention and not the 9 year old... Still not right for them to do - but if they do know better, and they should it could have been somewhat intentional. Talk to them and find out where they were coming from. It could have been just a case of not knowing their own strength (my boy is famous for this) or passive agressive behavior. Whenever someone does something to me that I dont like, I always try to look at myself as well and see if there was something that I may have been doing to "bring it on". But bottom line is there should be some converstaions and consequences. They are all lucky to have such a caring grandma!