First time I saw a boys hard penis

I travelled up from Cornwall with my parents too Slough on the ourskirts of London, where friends of Mum and Dad lived. Whilst my Mum and Dad sat in the front room talking to their friends. I went upstairs to play with Zoe and David. Zoe was my age and David was about 18 months younger. I had never met either before but were both quite welcoming. Zoe's bedroom had a wardrobe/office space, where the roof sloped down on the outside. We were playing there, Zoe pulled out a first aid kit, which had bandages and stethoscope amongst other things. We took turns being bandaged up and tried the stethoscope on each other. Zoe sugested that we should be doctors and David our patient. I went along with it as it seemed a fun thing to do. Zoe told David to wait outside the room as we got things ready. Zoe laid all the medical equipment on the desk and asked me to fetch David. I called him in. Zoe sat on the swivel chair at the desk and I sort of stood next to David. Zoe told David to take off his t-shirt so we could listen to his heart. His did as he was told and stood in just his shorts as first Zoe and then myself listened to his heart beat. Zoe then told David to remove his shorts and stand in just his underpants. I was a litle surprised at this sugestion, but David responded quickly and took his shorts down. At this point I had a feeing they had played doctors before. David stood their, his skinny frame and just his underpants. We pretended to take his blood pressure and both took turns listening to his heart beat. Zoe asked if I knew what was wrong with him, too which I just shrugged my shoulders. Zoe said we need to examine him fully, then told me to pull his pants down. I really wasn't sure and stepped back, Zoe seemed to get a bit angry at this point and pulled David towards her on her chair. She grabbed at the waistband with both hands and pulled his pants down, until they dropped to his ankles. She turned David side on, so he was facing us both, I had seen naked boys before, but David's willy was sticking up in mid air. It looked kind of funny they way it just stuck up like that, but I couldn't take my eyes off it. Zoe asked if I had seen a boys willy before, I said I hadn't seen one this close up. Zoe lifted David's penis and pointed below, 'that's his balls' she said. 'Go on Louise examine it!' Zoe encouraged me to touch it. I hesistated bit Zoe seemed to have a bit of a temper on her, so I did as she said. I touched David's willy it seem to harden even more as I felt it. Zoe told me to feel his balls, as I touched them them seemed to bunch up tighter. Zoe came forward again and said 'this is the best bit'. With that she pulled the skin on his penis back, exposing the very pink looking head of his penis, which has a little slit at the very tip. Zoe smiled as she seemed to enjoy showing me her brothers penis. Just at that moment Mum called up to say that we were going and I needed to come down. Not sure what would of happened if we had more time to play, I guess I will never know.