Child able to extend time on his own. How do I fix it?

My 12-year-old son has discovered that, on Norton Family Free version, he can select "Extend Time", type gibberish into the email and password field (seriously, there doesn't even need to have an @ sign or a .com in the email field) and Norton will simply say "We don't recognize your info, we'll send your parent an email" and let him stay on as long as he wants.

 

Surely, this is not the way it's supposed to work? How do I get it so that, when he does this, it says "Sorry, wrong info. You're locked out'? 

 

P.S. Even if it does send me an email (as it is, I get so many from Norton that I can't keep track), this does me no good if he wakes up in the middle of the night and decides to log on (which he's done).