What if grandparents have custody of Children?

There is not enough information provided to answer.  What do you mean "custody"?  Is there a court order of guardianship?  Actual custody order in favor of grandparent?  The kids just happen to have been there for some time?  Is there a divorce ongoing?  You are going to have to have a much more in-depth conversation with a family law specialist, revealing what has happened previously, to get any useful guidance.  Meantime, the information and linked statutes and other materials here might be helpful to you: http://willicklawgroup.com/child-custody-and-visitation/