I work for private aviation. We always require a poa for any minor whether for domestic or international travel. We've never had to use it but it is best to be prepared. You never know if there could be an amber alert or a medical issue.
We have the parent give the traveling adult permission for medical decisions, give the child permission to travel with the adult, list travel dates and locations, and contact info for both parents. I googled to find a form to base ours off of.