The following is a complete sample that you can use for your situation and adapt it however appropriate.
AFFIDAVIT AND POWER OF ATTORNEY (SHORT FORM)
I/we, (name of absent parent), the natural parent/legal guardian of (name of minor child), do hereby permit, allow and otherwise consent to the travel of (child's name), a minor child, on the (name of cruise line and ship) during the period (dates of travel) to be accompanied and escorted by (your name.) Further, I also affirm that (your name) has full power of attorney regarding said minor child in all matters, including but not limited to, medical, legal and all other manner of responsibility and that my full and express permission for all of the same and foregoing is hereby granted.
Further, your Affiants sayeth naught.
(signatures of person(s))
State/Commonwealth of __________
County/Parish of __________
Subscribed and sworn to before me, (name of the notary) this ____ day of _______200___ by (name of parent(s) giving consent.)
Signature of Notary
Seal of Notary
I hope this helps.
If in doubt, consult your family attorney.