My kids are pretty on top of what goes on in their personal area and others too....I should hope so since they are 22 and 19!
LOL!!
On a serious note, though I was very open and honest with them about anything they asked. I tried not to tell them more than what they were ready to digest at the time and just made really sure that they were comfortable in asking me anything they wanted to know. I think for us that was the key; setting the comfort level so they knew they could ask anytime.
Myown mother gave me a book when I was 12 and said, "If you read this and have any questions, just ask." I remember thinking WTH? I already knew most of it from my friends but I thought she could have been a bit more open about it. I later learned that she was simply uncomfortable talking about it and that was how her mom handled it so thats how she did it too.....
I vowed to make sure I was closer to my own kids than that...and both are very comfortable asking. This came in handy when my dd wanted to have birth control when she 17. It helped that we were already comfortable taking about stuff in that topic.