To wear or not to wear a neck brace is a matter of personal choice in the end, either for yourself or for your child. I wear a Leatt brace whenever I'm riding motocross, but I do not wear it when I'm trail riding moreso because of lack of ways to route my camelbak than anything else. I also have a 7 year old riding that has a small Leatt and he wears it when he rides all the time. I took a look at the Leatt Video's and research that went into designing the brace when I was making my decision to buy / wear one for the first time. I didn't go out and get one ASAP when they came out, but waiting a season and talked to others that had been wearing them etc etc. For me personally, (and I had been riding for 35+ years at that point) it came down to the idea of........ is it worth it to wear this item if it saves me from death / wheelchair just 1 time in a crash and I figured yes. Now I also know that wearing it may cause another damage in that same crash much like my CTI knee braces may transfer a knee injury to a broken leg, which many doctors and medical professionals say about knee braces. But I've had 4 knee surgeries already and know that my knees never worked as well after surgery #1 as before my first knee injury. I also know many people that have broken their legs (both femur and Tib / Fib) that have no re occurring problems after they are healed, but every person I know that has had knee surgery says that "it's never the same again". I wish I had been wearing knee braces when I got my first injury to my knees and could have prevented that even if it had meant a broken leg. My knees suck know and I do all I can to keep them working as best they can.
So I chose to wear a neck brace, not because I have ever needed it before in 35+ years of motorcycle riding / racing, but because if it saves me just one time from that MAJOR injury, it's priceless for the $395 that I paid for it. And the way I look at it, if I hit the ground hard enough to break my back / sternum or any other part of my spine with the brace on........ than I probably would have done worse without it on at that point.
That's my reasoning and the reason that I make my kid wear one too.