Yes, preparation is the key here, check for the Mcafee uninstall facility, download Avast, go straight to the Mcafee uninstall facility, uninstall it, reboot and ensure that it was a clean uninstall, the Mcafee software on your sons computer should have the uninstall option available however here is a link for you in case ;So as you are uninstalling one and installing the others is there a period of time where you are completely unprotected
http://service.mcafe...spx?id=TS100507
A matter of preference however if you uninstall it now and use Avast right away you will have no need to worry about having no protection when the Mcafee trial period expires.Would you allow the McAfee to stay until the free trial runs out?