BRL, understand completely mate, no insult or rudeness intended. There are a few people out there with issues connecting to WiFi after jailbreaking, but the normal fix is to reset network settings, or so my own research suggests anyway!!!
Another trick is if you son has anything like the app WiFiFoFum and is using that to connect to the WiFi. My iPhone 3GS certainly didn't like hooking up to the router using that app, but after I reset network settings it connected fine using the standard network connection through Settings.