Help on Panda antivirus and different user?

What does Windows Security Center say? If you're not protected, it should be going nuts telling you. If you're both logged on, I don't think Panda loads itself into memory on both accounts... as that would be an unnecessary waste of memory and CPU cycles. Try logging yourself out and then log in with your son's account and see what happens. I'm betting that with fast user switching, Panda won't load itself twice... and that you're still protected because it's running under your account.