It depends on where the children physically lived, regardless of legal guardianship.
If the children lived in the same home with you more than 183 nights, then you have a right to claim them as dependents. For example, this might be true if you, the children, and your parents all lived together for a while. The 183 nights do not have to be consecutive. In this case, you and your parents can choose who will claim the children. If you can't agree, you as the parent have priority over the grandparents, even if the children lived in your custody fewer total days than in your parent's custody.
If you did not live in the same home as the children for at least 183 nights, then only your parents can claim the children as dependents.
