Legally or developmentally? Legally, it depends on your jurisdiction, however, by and large, children need the permission/approval of both parents to leave the general area of their home... To travel internationally, they need a passport and the consent of both parents, unless one parent has sole legal custody.
I, Full Name, (mother|father) of Child Full Name to travel to (Destination City, State, Country) on (date of departure) with an expected return of (date of return). I may be contacted at (phone number including country code if traveling from overseas). I may have included a photo of my driver's license.
Recommended Consent Letter for Children Travelling Abroad. Information about travelling child. Information about accompanying person (leave blank if child is travelling alone) Contact information during trip. Signature(s) of person(s) giving consent. Signature of witness.
Non-U.S. citizen children traveling to the U.S. 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."
A consent letter demonstrates that children who travel alone, with only one parent/guardian, friends, relatives or a group (e.g. sports, school, musical, religious) have permission to travel abroad from every parent (or guardian) who is not accompanying them on the trip.
I, Full Name, (mother|father) of Child Full Name to travel to (Destination City, State, Country) on (date of departure) with an expected return of (date of return). I may be contacted at (phone number including country code if traveling from overseas). I may have included a photo of my driver's license.
Non-U.S. citizen children traveling to the U.S. 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."
Unless there is a legal order that states a parent cannot leave the US or otherwise travel without consent, then it's not required. Taking a child on a trip or vacation is never kidnapping in the absence of a court order that states otherwise.
It is not uncommon for a child to travel abroad with a family member or friend. However if you are taking a child abroad that you do not have parental responsibility for, you will need to ensure you have written permission from anyone that does have parental responsibility.
If you have sole child custody, the other parent may not need to sign the Child Travel Consent. In this case, you should travel with a copy of your court custody documentation. In addition, if a child has a deceased parent, it's recommended to travel with a copy of the deceased parent's death certificate.