It's great to hear about a young guy jumping into app development, you should be really proud of him (I'm sure you are!).
Those numbers, wow they are really disappointing. The apps I've worked with, we spend hundreds of man hours marketing them. Send me a message to email@example.com, I'll run a few things for your son (for free) and maybe can help him sell a few more units (and give you gusy some marketing tips). Still, once the "new" designation has passed, selling is tough.
We did sell some apps (since its not my app I'll leave numbers out) and had consistent sales for a couple of weeks, but those fell off after the initial blitz happened. We have numerous Twitter accounts that we've built up over time with a good, actionable audience and received thousands of clicks via our trackable bit.ly URL (that opened up the iTunes store). We also ran multiple videos that we distributed through multiple video sites. We had multiple thousands of views on those. The most traction we got was out of press releases. We spend $18 on one service and were picked up by hundreds of Mac/Apple/iPhone sites and were able to track that our release (only through the site's trackback service) had thousands of views. If your son is on Facebook, he should promote his apps through there also.