Overkill however if you want to [cover all the bases](http://traveltips.usatoday.com/forms-need-son-travel-someone-else-108821.html):

> **Consent to Travel**
> 
> In the United States, children do not usually need to carry a written
> consent to travel. If the courts are involved in the child’s life, his
> ability to travel might be affected. Both parents should sign a
> notarized consent to travel. You can download a form online or create
> your own. Specify the child’s full name and address, the names and
> addresses of both parents, the names and addresses of the adults
> traveling with the child, the authorized destination countries and the
> dates of the trip. 
> 
> **Medical Consent**
> 
> A medical consent form gives the accompanying adult the right to
> authorize medical treatment for your child while he is away. Some
> people combine a medical consent form with a general consent to travel
> form. 
> 
> **Temporary Power of Attorney**
> 
> If the trip will include activities such as parasailing or dog
> sledding that require parental consent, consider signing a temporary
> power of attorney. This is a legal document that gives the child’s
> adult travel companion the right to make virtually all parenting
> decisions for the specified period of time. A temporary power of
> attorney must be notarized.