Lovely sharing of your day with lil sis. One thing especially got me thinking.

She asked me if she could see my penis . . . I of course I said no . . . I admit I had a hard-on when playing and when she was on top of me, so I wonder if she at some point noticed?

and the secrecy of sex begins and continues for lil sis (for as long as we can force it on her) When should sex education start?

That's a highly likely assumption that that was the reason for her question. Of course, she noticed. A direct question deserves a direct answer. Would it be better, for her to say 'yes', show her (it would only take a second, she just ask to see it). That might be it for now or she might ask another question. We would be better daddys and big brothers and uncles and friends if we didn't put up these 'snack' diversions so easily. What if she then asked, 'why did it get big and hard?'. How many of us are prepared to give her a clear, concise answer. Not many, I suspect, because we are much better at avoiding the question.

I'm a conservative. I don't think you should have sex with your lil sis. But there is a difference between sex education and sex. You don't have to tell her everything all at once. There could be a day when you could properly tell her that you are a pedophile and actually enjoyed talking to her about that stuff and enjoyed showing her your stiffy. We have great responsibility to our little friends as pedophiles. Answering yes to her question might not be the right thing to do but it should be 'on the table'.

Dad in the other room might have another opinion. Or he might be a smart guy, who knows.

But, you did the right thing, given the piss poor attitudes about sex by sexual beings in the world today.