I have no experience of this myself to offer, but the world has suddenly changed in an alarming way for this little boy and he is angry and afraid.For all he knows, both parents may suddenly disappear. It affects all children badly, but they don't all show it in the same way.Some children appear quiet, but are just as upset inside, while others throw things.If it hasn't already happened, both parents need to talk to him [but not a long rambling discourse] telling him that Mummy and Daddy love him but Daddy has to live in a different house. He will still ask 'why' of course, but if he sees both parents a lot will learn to live with it.The other thing is that the parents need to be 'nice' to one another when together, and the children are present, and not say bad things about each other to the children either.That is often sadly not the case.You, the Grandma, represent safety and normality, and have to be understanding, because divorce is a huge trauma for young children.Hope that things get better for you all.