okay so some answers i got from the book " Questions Children Ask" by Dr. Miriam Stoppard are as follows:
Q: What is sex?
A:
for ages 2-4 = it's a special sort of cuddling that mummies & daddies do to show they love each other
for ages 4-6 = it's one way that two grown ups who love each other, like mummy & daddy, can get as close as possible to cuddle & kiss in a special way, usually in bed. Sometimes a man & woman can start a baby when they have sex.
for ages 6-8 = it's one of the ways that two grown up people can show that they love each other. Sex is the time when they can make each other feel happy & wonderful. When we talk about sex in this way it is short for "sexual intercourse". There are lots of slang words for sex but they're not polite. During sexual intercourse a man's penis get's stiff and he puts it inside his partners vagina, which feels nice. Having sex can start a baby, but it usually doesn't because grown up's generally have sex as a way of showing how much they love each other, even when they are quite old.
HAHAHAHA gosh, is that not a bit too much to tell a 6 - 8 year old? what do you all think?

i was a bit in shock after reading that one.