Talk to them before they hear the mature content from somewhere else and especially if that information will be inaccurate. Better that they hear it from you first.
But this doesn't have to only be about 1 year accelerated kids. The problem is similar when there is a red-shirted kid (did I say that right?) or there are some kids in the class that watch unsupervised TV/internet and it can get bad.
Sorry, not much help here. A private school classroom isn't going to solve this problem as some of these kid discussions/talks probably do not happen in-class.
