Can our son bring our grandchildren to visit us?

If your son has custody/visitation rights, and there is no court order that prohibits him from leaving his home state with the children during his custody/visitation time, then he can bring them to visit you without any repercussions. He only needs to notify their mother as to the details. I am unclear on the part about the children's mother wanting to take them out of the country. That requires passports, and she will need his cooperation to get passports. He does not have to cooperate if he believes she is a flight risk. If he has no custody/visitation orders, he needs to get that done to clarify his rights and make them enforceable.