When can a grandparent sue for custody of a grandchild left in their care?
Parents, particularly younger ones, sometimes face temporary changes of housing or temporary job or military assignments, where they may need grandparents to care for their child. Sometimes the parent will give the grandparent legal forms such as letters of temporary guardianship, to allow the grandparent to handle school and medical matters, but without actually transferring custody to the grandparent (which would require a court order to undo).
Generally, temporary arrangements like these should not by themselves provide a basis for a grandparent or any other non-parent to sue for permanent legal custody of the child, over the objection of a parent. For a non-parent to sue for custody, they must first prove the parents to be unfit or to have abandoned the child, or similar extraordinary circumstances. Only then will the Court consider whether it is in the best interests of the child for a non-parent to have custody.
If the parents stay appropriately involved with their child during temporary relocations or assignments, there should be no finding of unfitness or abandonment. However, if the parent stops communicating with and planning for the child, or if the reason the child is with grandparents is because the parents are mentally ill or abusing drugs or alcohol, a court could find the appropriate extraordinary circumstances to exist that allow the grandparents to sue for custody, at which point the Court may conduct investigations and would hold hearings to determine if it is in the best interests of the child for custody to be awarded to the non-parent.
All of the above is in contrast to the situation where a parent leaves a child with relatives and the other parent sues for custody. As opposed to a non-parent, the other parent does not have to first prove extraordinary circumstances in order to sue for custody of their child. Assuming, in the case of a father, that paternity is legally established, the parent automatically has legal standing to sue for custody, and would go directly to proceedings about what custody arrangement is in the child's best interest; the only other legal hurdle a parent might face would be the need to prove a "change of circumstances" from a prior custody order, for example, if they are seeking to change custody from the other parent to themselves.