This all depends on the router you have.
Some routers have the security key (WEP, WPA etc) printed on the router itself.
sometimes the routers are wireless capable, but not set up with any security.
Who is your internet provider? and what make of router do you have?
Depending on which games your son is likely to play - it is a better idea to connect the Xbox directly to the router with an ethernet cable.
the speed is much faster through a cable than it is wirlessly.
If the router and the Xbox are not near each other - you can get a device called 'Home Plugs' - these use your electrical ring main as a network.
buy a pair of these plugs, plug one in near the Xbox and the second near the router (not in an extension lead, directly into the wall socket)
you will need 2 ethernet cables - these will go from the plug into the Xbox and from the plug into the router.
These plugs can usually be bought from good computer stores or on line at places like ebuyer (www.ebuyer.com) - check for wired networking or home plugs