Some parents show concern over when their kid learns about homosexuality.
But in all honesty, how many show any concern over the fact that often, it is neither the school, nor a homosexual, nor the parents who give the child their first exposure to the concept of "homosexuality" to the child.
It's the fellow class-mates.

Polls have shown that "fag" is a very common slur amongst kids. The negative condemnation of gays comes early as a school-yard societal "lesson".

Quite frankly, on some subconscious level (or possibly very conscious) I think some people who don't want "gay" in the main-stream would very much prefer that kids learn the word "fag" before they learn exactly what that means. Obviously not true of all, but one has to wonder about parents who kick up quite a fuss over a "gay" book, yet not a mention over what the other kids bandy about the school-yard.
And mind you, I am talking about EXACTLY what "homosexuality" means and not the distorted stereo-typing and prejudiced statements that often get bandied about like some Oklahoma politicians, or by schoolyard kids...

To those parents who want control over when their kid learns about such things, please be painfully aware that more than likely that you will NOT control when your kid learns the word "fag" (unless you're of the Fred Phelps mindset and you're the one teaching it to the child).

A responsible parent would not want their child to learn such misconceptions like "you can't get pregnant on the first time" or "jumping up and down afterwards prevents pregnancy".
They would want to teach their kid the facts before the child "learned" such things from other class-mates.

Considering how ridiculously prevalent hearing slurs like "fag" or "that's so gay" are in our schools, parents might want to consider that in deciding the "right time" to talk to your kid about homosexuality's existence, unless you're comfortable with the slur "fag" being the first thing your kid learns on the subject...