Good advice. I also think the real reason is the exposure to the intenet. Not only because of predators, but because of interaction with strangers in general. Actually, if you look closely at released games with age ratings, the online interactions with other players is usually not rated, like this: Online Interactions Not Rated by the ESRB (PC).
And those stranges do not even need to be adults. Kids can be cruel. Taking abuse from a fellow player is another thing than getting bad comments and ratings on your game and art. This is hard for adults too.