My children's grandfather is very good at sports and balancing and has been riding onewheels for as long as they've been around. My kids learned from him quite a while ago. Couple of years ago they each got a Pint from grandmother as a gift.
They always wear helmets but we had a hard time getting them to wear wrist guards, that is, until one of my kids pushed it to the limit downhill in a park, rode over the pebble, wiped out and broke his wrist. His app said he hit 17mph. Since then, there hasn't been a ride without helmet and wrist-guards and they ride around quite a bit, to a store, around the city, to the park, just for the hell of it.
Breaking his wrist sucked for him but was a great teaching moment for the rest of his life, to wear right equipment for the job.
They always comment on people tooling around without helmets on those wheels or scooters. We as parents have a small success right here.