Yes, I've seen my dad's cock several times when I was a child.
Since he was living in a house undergoing renovation in the countryside at that time, we used to pee outside next to each other during summertime.
But the most vivid memory I have of it is when he showered with me (since I was too young to shower on my own). Not the biggest cock ever, still a nicely-sized entirely-shaven slab of meat, definitely bigger than mine today. I guess it was more impressive with child's eyes and my face was literally to the height of his crotch. I remember I was low-key afraid of looking at it. ;D