L.L.
this is a very hard thing to deal with he will miss his grandparents and his routine.Talk to your parents about the possibility of setting up regular vists for him maybe a whole weekend, Then get a calendar and mark the days, this will give him a way of "seeing " when he gets to be with the Grands again.And never use these visits as a bribe or take them away for punishment,He would noy be able to understand that,They have been a big part of his life.Kids love routine and he may just be afraid of the change,when he sees that they are still apart of your lives he will be Ok Good luck!!! L.