Between Rufus and Bostjan you've already received some great advice. I'd add just this.
You can look online at any number of sites and see pictures of finished and detailled tanks for inspiration. Just keep in mind most of what you'll see are produced by professional or highly skilled modellers who have invested a substantial amount of time and money in getting those results. Don't let your son become discouraged that his results don't match theirs.
Here's a pro build of a M10 and its cousin the M36:
You know what I'm saying. Don't let him get hung up on it so that he thinks he's lacking what it takes. If he has fun and enjoys building the kit he'll hopefully want to build another and another and the rest will take care of itself. Just keep doing what you are doing by helping him where you can. Tell him he's doing a good job or encourage him to do better for those moments when even he knows better.
This is actually the binary group where model pictures are posted. The actual discussion group is rec.models.scale. My reply will be crossposted there so that others can offer advice and opinions. There's a lot more guys like Rufus and Bostjan on RMS that will be eager to help should you have further questions on this or future kits.
Hope that helps,
WmB