Saftey Gear.
Well some may agree or disagree with me but I have 3 kids that race 8 and under. So this is my take on it.
HelmeT! Good one. DOT AND SNELL approved. Just DOT is not as good. You can get a good M2R helmet for $80 if you cannot find locally let me know. Don't buy used here!
Boots: Used is fine. Unfortunatley the higher end boots have better features like bracing and padding. Usually you can find nice ones for sale at the track from guys that grew out of stuff.
Pants/Shirt/Gloves...of course.
Knee pads: really helps,
Elbow pads:
Chest Protector: Might not seem importatnt but my little one crashed so hard he broke the back panel and ended up with only a little bruise directly on his vertabrae. He also wears a pad under his chest protector we got from YPG
http://www.youthprotectiongear.com/
My kids also wear the padded under shirt which has pads on the ribs and lower back. Then some padded shorts that have thigh and hip pads too.
Neck Collar. Their has been debate about wether or not they help protect from collar bone breaks but at a minimum they keep the neck from compressing during a crash landing on your head...also they help with fatigue from wipping around your head.
MOUTH PIECE! Especially if he has his grownup teeth. Not many people do this one but if you think about it it makes sense. Basket ball guys are starting to wear them...their contact doesn't even come close to a crash.
My 4 year old wears everything mentioned above. He has crashed some pretty good crashes and not really even had a scratch. My 8 year old has pretty much added a piece of gear each time he crashed and we realized something wasn't protected. The thing is now he doesn't even try to skimp on the gear. Since it has been the ONLY way he can ride since we bought everything its a non issue. A few times he forgot his knee pads because he does not like to wear them. I make him strip all the way down and put them on. A few times doing that and he remembers now because I don't bend on this issue.