Anthony, the most well-regarded instant messenger for Linux is probably Pidgin, however this does not have webcam support. Nonetheless, there are several successful clients out there that will filful your requirements.
Here are a couple of IMs that offer webcam support (in no particular order):aMsnKopete
Emesene offers webcam support in their developmental version, and KMess is planning on developing this feature. At the end of the day, it really boils down to your son's preference - the actual abilities of all these clients is comparable, so personal preference is really the deciding factor.
**Please be sure to download these applications from the Software Portal
, to ensure that they are appropriate versions**
It's good to hear of such a young user of Linux