Riding one illegally is incredibly stupid but it's great you're advocating for a father to buy his seven year old son one so he can be a law breaker too.
Right. He asked if anyone had advice on them or something similar. I along with a few friends commuted to work on electric unicycles over the last 2 years and none of us have ever had our PEVs confiscated. If you ride them sensibly and don't act like a tit, the police have actual issues to face rather than give you a talking to. Now if you were riding into property or people and being a danger to yourself and others it would obviously get taken away. I don't know where in the country you are but down here i see people riding by electric scooters, unicycles, skateboards and OneWheels pretty much daily as a means of getting to work/ditching the car. Never once saw anyone getting a talking to and never in my 1000+ miles did i ever have even as much as a glance from the police and i rode past a station each morning.
Regardless, clearly his seven year old son isn't going to be riding on roads so not sure why you have the attitude.