That's how we grew up and we wish everything remained the same way even in 21st century.
But world has other plans for you.
Economy opened up
Dogs copulating in the middle of busy Indian roads to our beloved cultural pinnacle, Bollywood! everything in the universe conspires to make them aware of most primal instinct of our being....reproduction and its wonderful tool ..SEX
If this was true, we wouldnt be 1.3 Billion Indians from a few "cultured" couples :)
They are also curious about body and do not hesitate to point to your (or a stranger's) body parts and ask difficult questions.
2. There is no right age to ask a question
4. If you don't satisfy this curiosity, they WILL find other ways...inconvenient, embarrassing, shocking and may be harmful ways.
That's how it works.
1. With a pleasant smile or a very straight face, matter of fact way.
2. Brief, quick answer. (long winded answers are for PhD thesis and for liars)
3. Factual not value/judgement laden (neutral tone helps examination of beliefs)
no matter how shocked you are, ask with a smile "what do you mean by that" "whatever made you think that?"
mostly the answer will be honest and cute :)
When children ask stuff like - "when can i have sex?" or something similarly shocking, tell them "When you become adult" with a straight face. Children understand age related privileges like driving, job very well. This is a safe and correct answer.