Norton AV is not freeware so anyone giving it away for free (or very cheaply) is most likely distributing a pirated version.
But I've got a better idea. Forget about Norton and try AVG instead.
It uses fewer system resources than Norton, catches more viruses, and did I mention it's free.
You can get the free version of AVG
here. (Remember to uninstall any other AV software before installing AVG.)
If you want to renew you son's license for Norton AV I suggest you buy it directly from
Symantec.