I also think it a bit ridiculous to be talking about how children should behave at a funeral and how they should be acting. Everyone, including adults grieve differently, I've known heaps that go off the rails when a loved one dies - myself included. There is no correct way to grieve.
I think far too often people just assume that kids don't get it, or they aren't saddened or grieving because they are still playing. But that just is not the case at all.