It depends on the state. Here are some general points: First of all, the natural parent, until his or her parental rights temporarily or permantently revoked by a court, always has custody rights superior to those of any other relatives, regardless of any voluntary agreement he or she may have signed. Secondly, agreement for custody, whether or not drafted by a lawyer, should have been presented to the court of appropriate jurisdiction to be approved and the court should have issued an order, granting guardianship/custody to the grandmother. Finally, the grandmother can petition court for visitations if her bond with the kid is strong and keeping her away from the kid would be harmful to the child (however, this standard varies from state to state). The granny can also file a petition for guardianship, but for that she'll have to show that the parents are unfit to care for the child, and that is another very high burden because the natural parent will be presumed fit unless otherwise proven (the parent abandoned the child, continuously engages in behavior harmful to the child, knowingly puts the child in danger, etc.) Consultation with an attorney would be helpful! Good luck.