S.H.
Also look into this:
It is called "Child Travel Consent Forms" or
"Affidavit of Parental Consent" .
It has to be notarized.
If you Google Search it, you can find free templates of it.
Such as:
http://www.documatica-forms.com/usa/child-travel-consent/...
We used this when my Husband traveled with my Daughter.
Our Travel Agent said it is required. Some airlines etc., will ask for it.