Well when I was 9, I was at the swimming pool with my mom, and she was watching from the seating area.
I had to pee and being scared that the water actually changed colour if you pee in the pool, I went to the urinals in the locker room.
There was a guy in there, looking back he was clearly crusing, who had an erection at the urinals. He had a big mushroom head cock and I'd never seen anything like it and stared like a kid does while I peed, and the guy made no attempt to hide it.
Seeing that the coast was clear, he told open my mouth and bent my head gently down onto his cock. I could barely fit the head in.
He thrust in my mouth for a few seconds but got spooked by footsteps or voices or something and left. I was pretty confused by it but went back to the pool fine. I remember my mom asked why I took so long, and I just shrugged it off and never told her anything about it.
I was in the bath probably days maybe weeks after, and my dad came in to pee, and catching a glimpse of his dick, I was reminded of what happened and asked him why would someone stick his thing in my mouth. I remember actually saying my mouth, and him instantly figure out something happened.
He grilled me for awhile but I said it didn't happen, I just thought of it. He didn't seem to believe me and left. I thought I was in big trouble but it didn't come up with my mom or anything.
Then the next week on a bath night he came in again, asked me the same questions about it while he was "peeing" but noticed he was getting hard and stroking it.
Eventually he walked over to the bathtub I and asked "did it look like this?" And I nodded, too scared to loe by this point.. though my dad was a longer dick with less of a head to it.
It wasn't long before it was in my mouth, he didn't do anything at first, I think he wanted to test if I'd be sucking someone's dick properly. Obviously I had no idea what to do and he basically started moving my head up and down on it.