When I was growing up my sister who is a year younger than me shared a bedromm until my young brother, 10 yrs my junior came along. We were like most kids shared a bath together until we ere about 10 and there was not much privacy in our small house. The olds would walk aroud the bedroom naked but rarely the rest of the house. Sis and I used to change for bed etc in our room and it was obvious there were differences but it was all so natural. I would sometimes get a flash of her pussy lips and the hidden delights but wasnt really aware of the pinker bits just that it was getting more of a buzz to look at them. Her boobs were just starting to develop and she would shake them at me but there wasnt much to shake.
I had decided it would be better to spy on mum to see the women bits she had real boobs and a good covering of dark hair in a triangle covering her bits - anyway to cut a long story short I was peeking through the bathroom door at her in the shower when my sister caught me, thought I would be totally busted but we came to an arrangement. Sis had the same idea as me, she had seen my doodle with its sparce covering of hair and decided she wanted to see a real one. Next time the old man was in the shower she came and told me and it was my job to get something from the cupboard in the bathroom and leave the door slightly open. I carried out my part and left her squating against the door watching him in the shower.
That night we talked about what we had seen and agreed we both had a bit of growing to do , she asked me if I had seen dad big, I hadnt.
Shortly after she moved into the new bedroom and my young bro moved in with me. We did not have sex with each other or watch each other wank, although I used to and still do regularly - we just have a good relationship.
We still joke about what we got up to at family gatherings, but just between ourselves.