Are the adults on the boat while the kids are driving? If so this is completely legal. Here is the exerpt out of the NH Boating Laws :
https://www.boat-ed.com/newhampshire...erate-a-Vessel
"A vessel powered by more than 25 horsepower (other than a “ski craft”) may be operated by:
A person under 16 years of age only if he or she is accompanied by a person 18 years old or older who has a valid Safe Boater Education Certificate. The accompanying person is responsible for any injury or damage caused during operation of the vessel."
My kids love driving the boat, in very safe and secure areas where there is not a lot of traffic or navigation to be done...