As
@osu1978 said, wearing gloves for protection is prudent. Don't assume he will never crash, you'd likely be wrong. It's a reflex to put one's hands out in front of the face on the way down, if there's time. Expensive motorcycle riding gloves are best, however any gloves would be better than none, even the cheap synthetic ones I'm going to link below (I bought a pair for bicycle and casual minibike rides, cheap enough not to care if I were to lose them). Riding gloves should fit snugly so they don't wrinkle (causing discomfort), squirm around or come off at a bad time, retention at the wrist is a good feature.
https://www.amazon.com/gp/product/B077NX89YY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
There are countless choices in aftermarket grips, too soft (squirmy foam), soft, medium, hard. Barrel shaped grips can make it easier to twist the throttle and reduce fatigue due to the larger diameter in the middle of the grip. I'll post a link to some barrel-shape Kraton (somewhat soft but not too soft) grips as an example.
https://www.amazon.com/dp/B014MZ8U8C/ref=nav_timeline_asin?_encoding=UTF8&psc=1
I have seen in your other thread that he has a full-face helmet, kudos on that. Make sure it fits properly, should be very snug to prevent it from twisting on the head on impact and make him always snug the chin strap, a loose fitting helmet can break a neck. I wouldn't be typing this if I hadn't been wearing a full-face helmet when I crashed a motorcycle 31 years ago. Consider some more riding gear. Elbows and knees are rather vulnerable, I broke my left elbow in that crash, big hole, big chunk of bone broken off; the surgeon called it "an impressive wound". Had to have a second surgery later to get more function but never got full range of motion back. I also had road rash on my chest, stomach, shoulders, arms, wrists, knees (you get the picture) from sliding down the road. Check the link below to get an idea of what off-road type gear is available; not a recommendation for the retailer (I've had no dealings with them), just using as an example.
https://www.cyclegear.com/dirt-bike-protection-armor
After that crash, it was a few years before I bought another street bike. When I did buy one, I also bought a new Shoei helmet, a (special order) $750 Vanson jacket for warm weather, dove gray (much cooler than black in sunlight), fully ventilated (perforated leather), full armor including optional segmented hard spine protector, also a Fieldsheer black leather full armor jacket with thermal liner for cool weather (it was a more upscale brand than what it appears to be today, I think the jacket was around $300-350 retail); also bought Kevlar reinforced leather gloves with carbon fiber knuckle protectors that cost more than some cheap leather jackets. Fortunately, I had a friend at a local motorcycle dealership who gave me a big discount on the gear (I paid a little over $500 for the $750 retail Vanson jacket for example). I had learned, the hard way, about the cost of gear relative to the cost of not having it when you need it. Am I suggesting you buy several hundred dollars worth of gear for riding a minibike? No, just trying to provide some perspective. Even inexpensive gear would be better than none, something like the Built Amped Jacket should provide a lot of protection for little money (such a jacket should fit snugly to keep armor from shifting around).
https://www.cyclegear.com/gear/bilt-amped-jacket
Riding a minibike may not be the same as riding a street bike but wearing some riding gear is wise, a properly fitting helmet and gloves at minimum but also consider additional gear, especially for your kids. You can always give them the timeless "Don't do as I do, do as I say!"