Hello Elaine Edwards,
I have a section at the bottom of my waiver for the parent/guardian to sign when the client is a minor. ACE also has forms geared to the youth:
The American Council on Exercise
4851 Paramount Drive
San Diego, CA 92123
Natalie aka NAPS 2 B Fit.
A few things to consider
Does your liability insurance cover minors?
Do you have CPR for minors?
Do you have a specialty certification for teaching to youth?
If you are a member of IDEA you can contact them directly or look on their website
I know as an ACE certified Health Coach I am privy to such.