I think it is as most other things in life,
it depends how when where and under what conditions you use it.
We are responsible for our children and must heed to that responsibility. there are parents that undrstand this, but nevertheless trust their children. Those are the times that the yetzer horah comes and talks to the kids little by little, telling them things like, “its ok just look, for a second over there” etc etc.
I dont really understand why parents dont have the “J-NET” or other types of controlled internet usage. i know sometimes you can over ride these controls, but in the general it works. As many other things in life you should do the best you can and a heartfelt “kapital tihilim” can accomplish so much.
May hashem bestow upon all of our teenagers and children that we should be spared from the yetzer horah and stand strong in yiddishkiet.
chazak uboruch