I've not commented for quite a while because I have 5 kids and have been accused of being overly protective. Also, I truely hope the little guy comes out okay.
Way back when my 16 year old was 7, I had an ATV and he loved to ride it with me. I began teaching him how to drive it with me behind him helping him along. Much to my surprise, he suddenly jerked the front wheels to one side and hit the throttle. He later explained he saw that done on TV. He was trying to do a "donut". The ATV flipped. I held onto the handlebars and kept my feet firmly planted on the foot pegs and created a "safety cage" around him as it went over. It worked well for him, but broke my left femur. He was uninjured.
I sold the ATV and really worried what a 600 pound ATV would have done to him. Since then, it seems "all" of the neighbor kids have gotten ATV's and my kids want to go riding with them. My compromise was to buy the Kubota RTV, and later, a Yamaha Rhino. Although nothing will be completely safe, both of these vehicles feature fully certified ROPS and safety belts.
Again, I hope the little guy comes out okay. I'm just a doting father and am paranoid about knowing what a 600 pound ATV can do to a child. Please don't take this post as preaching, because it isn't. I know how bad the kids want to ride - I raced motocross for years as well as having several ATV's - but I really think kids under 16 shouldn't be on an ATV, especially if it doesn't have a roll cage and seat belts.