Totoriko:
As a parent (I assume you are since you're so experienced with them) you should know how to control your kids.
Nope, not a parent...or at least I hope I'm not. Since I'm only 19, I was talking from experience rather than as a parent.
Your children will just want to push away from you if you attempt to be over-protective by monitoring their internet usage, making sure they're home as soon as school finishes and whatever else. I'm not suggesting that parents should join in with what their children are doing, I'm saying they should (unless it's
deadly serious) let it slide.
The world is how it is - Growing up in rough areas, going to normal schools, the internet... It all comes together to force people to grow up (or at least try adult rated things) faster than parents would like.
...Anyway. Playing most 15/18 games and watching most 15/18 movies will not corrupt anyone. The ONLY time I'd think it wrong for a kid (if we're talking pre-teen) is if it's a gory/disturbing 18+ horror, but aside from that...
Who gives age ratings? Most certainly not a divine being who knows all, just another person who puts a number on that others accept as correct without thinking. Those ratings can be seen as nothing more than the recommendations of over-protective old men.