i have one way that costs nothing
first, you need your sons computer
next, go to start, then run, type in cmd or command, a dos window should pop up
type in ipconfig
a list will appear
i that list, find the ip adress
note it
then go to start menu, right click it, go to properties go to system properties
click on allow remote assistance or something
save it then leave
go to your computer go to start menu
go to accesories, goto remote desktop connection
and you should have your sons screen up
i haven't tested this myself, but try it