"What do I do if my child doesn’t get returned to me after summer visits?!"
It depends on whether the child was born during a marriage.
If the child was born during marriage and you and your spouse are separated but not yet divorced, and there is no other court order in place, then you are considered joint custodians and have equal rights of access to the child. So, if you are the parent who wants to keep the child but the agreement was to return the child, then you should file for divorce or custody to get a court order legally allowing you to keep the child. If you are the parent who wants the child returned, then you should file for divorce or custody to get a court order requiring the other parent to legally return the child.
If the child was born outside of a marriage, and there is no other court order in place, then until a court legally establishes paternity, the mother is the custodial parent. So, the father must file a paternity action to establish rights to legally keep the child. Otherwise, the mother is legally entitled to the child.
The police will not get involved unless there is a court order in place, telling you this is a civil matter and to seek the services of a lawyer.
It is not considered parental kidnapping or interference with child custody unless you are in violation of a court order.
The child doesn’t get to make the choice, so the parents must obey the court order. Failure to obey the court order can lead to a contempt action being filed against the violating party. Being found in contempt means the court order for custody and visitation could be modified, or changed, and the violating party can be fined and/or put in jail. A contempt action is filed in the same court where the original custody order originated.
Remember that if there is no court order, then the parties can agree to whatever arrangements they would like.
So, if you don’t know what to do, then you should seek the advice of a lawyer, to avoid potentially negative consequences to you and your child.