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."
Passport and/or birth certificate. Proof of relationship to parent or guardian. Travel itinerary and addresses for accommodation. Child Medical Consent form to give another person authority to make medical decisions on behalf of the child.
You can obtain a travel consent form online where there are many templates that can be downloaded. Alternatively, if you require a more bespoke travel consent document, our team of notaries can assist in drafting one to your requirements.
To whom it may concern, I (mothers name) -- UK Passport Number , natural mother of (Son's full name) born on xx November 2001 and (Daughters full name) born on xx September 2004 hereby give full permission for both children to travel with their father (my name), UK Passport Number x wherever he might decide ...
A parent generally needs permission from the other parent before travelling with the child especially if the travel will impact the parenting time of the other parent. However, if the separation agreement dictates how travel should occur, both parents are expected to follow the terms of the agreement.
In the USA, though, unless there's a court order requiring permission from both parents, a child may travel (even to overseas) with either parent/guardian without showing proof of permission from the other parent.