That is the kind of case that lawyers pray for. It sends the kids to college and the family to the Bahamas for Christmas.
Waivers work best if the person is waiving something that exists.
If there are no well-fitting helmets available in assorted sized it is difficult to maintain that the waiver had substance. It is hard to waive the use of something that isn't available. There is a similar problem with the helmet waiver buried in the primary release form. That has the function of making the customer waive the helmet if he wants to ride. It is so much easier to put the helmet on the wranglers and guests and just go for a nice safe ride.