I just started coaching this year, I am one of 3 assistants to our head coach for our 3rd/4th graders team. I played football 10 years as a youth and won 2 state championships with my high school team.
After 3 weeks of practice (and one 1 week camp with the high school coaches) a few observations I have seen:
1. The kids have a TERRIBLE time remembering the snap count. Even when faced with extra sprints and up-downs, the kids are still jumping off sides all the time.
2. A lot of the kids have difficulty getting into a proper stance, whether it be 2 point or 3 point.
3. Lastly, exploding off the ball is critical, and difficult for many kids. It would help your son if you could teach him to get fired-up, and to not be afraid to lay it all out there every chance he gets when the ball is snapped. A lot of kids are just too timid for football - intensity is very hard to teach.
And CPA's tips on hand offs and holding the ball are fantastic. Those will both be critical skills to teach your boy as a RB.
Here's an easy drill for snap count. It may seem simplistic, maybe funny, but it works, at least in my experience.
First, at that age keep the snap count simple. A three cadence call. Wait until they get a little older for something more advanced (going on a silent count, going on 2). Do something like, "Ready...Set...Hut" or "Go...Set...Hut".
Now the drill. After they warm up, have them remain in their lines/rows. Pull the quarterback out (and any backups). Have the everyone, including quarterback, put up their hands ready to clap. Have the quarterback tell them when to clap "Ready", "Set" or "Hut". then go through his cadence. When he gets to the call he told them everyone claps together.
QB to group: "On Hut, on Hut"
QB: "Ready"
QB: "Set"
QB: "Hut"
Group:
clap
They need to all clap together. Have them do this 5-10 times in a row without a mistake. Have the QB change the count. Do it EVERY practice. Team needs to get used to the QB's voice and timing.
Also, make sure the QB is not altering his cadence timing either. The kids are expecting the Hut to be said after the Set at the same time, every time. No long pauses either. And of course, QB needs to be loud.
Stance: With your experience, you probably have a good feel for how a stance should work. Here's what I do: feet should be shoulder width apart, same side foot that hand is going down, should be slightly back. Have kids bend knees like sitting on toilet. Do not put hand down yet. Slightly bend at the hips, place hand down. NO pressure on the hands. If the knuckles are turning white his weight is not over his feet, which is where it should be. have him shift his weight back. I know this is counter-intuitive to firing out, but the problem is with their weight forward, they cannot move their feet quick enough to get into good position and then work their guy. With weight forward, they will tend to wiff/miss their guy completely.