My oldest (19) was told about them and to stay away period.
Please don't take this the wrong way, but - wow.
The rule in my house (the wife and I agreed upon this before our marriage) is that ignorance is NOT bliss, and that our children would be well educated in firearms. Locking them up and saying NO is the best way to stir curiosity.
So, from a very young age our daughter was told "any time you want to see, touch, clean or admire the firearms, just ask." Any time she asked, it became an opportunity to teach the rules.
She was also taught NEVER touch them without asking first. To be sure, before I had a safe, all had trigger locks. BUT, I don't believe she ever got into them without permission.
I did have to size up her maturity about the time she hit 8 or so, but that was when she fired her first rounds in .22LR. She's coming up on 16 now (Help Me, Oh Lord) and a few years ago graduated to 9MM pistols and .223 rifles.
For the last 6 years or so, she has NEVER asked to see the firearms, and rarely accepts my invitation to go shooting.
But she knows the rules, she knows how to use firearms, and has NO unsatisfied curiosity about them. And if she ever develops a new unsatisfied curiosity, all she has to do is ask.