Hi.
And just as well child can see a naughty picture on TV. Or a phone ad.
Or a magazine/newspaper. Anywhere, once you start thinking about it.
Whatever damage is done depends on child's state of mind, which is
influenced by his/her prior education. Which, for the most part, should
be (IMO) provided by parents first, and society (friends, school,
whatever) - second.
And internet censorship is not a substitute of education. The only
thing that censorship can teach is how to workaround it. Or that one's
parents are complete <insert_some_profanity_here>. Is that how you want
your children to perceive you?
Besides, what's up with this 15 years mark?