A letter of consent, preferably in English and notarized, from the other parent or signed by both custodial parents. The letter should say: "I acknowledge that my child is traveling outside the country with the name of the adult with my permission."
I, ______________________________________________ (name of parent), am the ______ (mother) ______ (father) of __________________________________ , aged ____________ , and do hereby give my consent for (him)(her) to travel with __________________________________________________________________ (name/address of traveling ...
It is not always required, however having one gives peace of mind for all eventualities. Any parent who is not travelling with the minor will need to sign the travel consent. They will need to attend an appointment with the notary and have certain identification documents.