memories

D has surprised me many times with the little things she remembers from growing up, often things I had forgotten
Last night we were chatting about an interview I'd seen where someone was asked where they learned most of their sex education. I said a wonderful biology teacher at secondary school. She was not much older than us year 2's and we'd have a discussion session once a week where we could ask her anything.
D then said 'I learnt about sex for a post it note conversation (write question/answer and hand it to other person) with you when I was about 10' the post its were because she was embarrassed not me

Why do I not remember that? I would have expected it to stick in my mind. I can recall many things from my childhood and my short term memory is fine.
Do you remember things like this ?