Now depending on how curious he is he may ask, But why abba do we have to get married to have children? If he asks this i feel the best way is to actually tell him and explain to him the biological reasoning behind it. Now on this i know many would disagree but i feel strongly about it.
Imtrying25, that was a beautiful post... But, with the particular quote above, although I respect your opinion, my personal opinion is that as soon as a child understands the biological process, he will have a lot more to "think about" than he would have otherwise. Once he knows, not only will he feel a natural attraction to girls - like you said, but he will
understand why and his imagination will take him places that it wouldn't have otherwise. Therefore, in my personal opinion (and everyone is free to disagree), it is best to delay telling kids the truth about the biological process for as long as it is possible. Obviously, if they find out from friends, there's nothing we can do, and in such a case we need to explain them more along the lines of what you wrote afterwards (about using it for Kedusha, etc...)... But, I feel that as long as we CAN delay it, why give them more to think about? Why should they be given a test to think of every girl they see in such terms, if they could be blissfully unaware of it for as long as possible?
Now there is some justified concern that if we don't tell them, they'll find out on their own in worse ways and won't tell us, and then we won't have the opportunity to give them hadracha about how it needs to be used right, etc... This is a good point too, but I still think that the first concern beats the second, unless you sense that it is inevitable that the child will be finding out ANYWAY any day...
As I have my own kids, ages 1 to 13, I have been thinking of creative ways of getting around the issue. If my kids ask me point blank how it's possible that parents only have kids when they're married, and how does it make sense that the kid looks like the father, etc... I have formulated a creative response that goes something along the lines of "married couples kiss, and when the body senses someone else's saliva, it starts the pregnancy process..." :-\ I haven't had to use this yet, but the day is probably coming closer... Just the other Shabbos, this topic came up and I avoided it somehow...
Yes, my situation may be different than others. I live in a
very protected environment, where my kids are sorrounded by only religious people, in a very chareidi community, and they don't see TV, movies or internet. Who knows, maybe in such a state I'll be able to get away with not telling them till the day before the wedding?
Although this sounds like a primitive approach, I truly feel that this is in their best interest. Being blissfully unaware of the process will delay the dangers of fantasy, masturbation, addiction, desire, etc. etc. And if I can save them all this by simply not telling, why not?
Again, not everybody's situation is the same. It has a lot to do with HOW sheltered your kids are, I guess.