Can a grandparent be charged for kidnapping?

I recently dropped my two daughters off at there grandfather house. I was supposed to pick them up three hours later. However, I did not pick them up until the next day. The grandfather called his ex wife (the grandmother) to pick up the girls. The grandmother decides to take the kids and keep them away from the mother. She did give me the phone number or address. Also, I have full custody of the oldest daughter from a previous relationship. Can either grandparent be arrested for this?