I was always interested in the human female form, even as a little boy. I would say my very first conscious memory of what a vulva looked like was when I was about 4 or 5 and in daycare.
Boys and girls usually went to the bathrooms in groups in those situations, it was easier for the adult minders to watch us all at once. My friend Erin took her turn to pee, and she lifted her skirt and pulled her panties down to her knees, thus giving me a full on view from across the room. To my young imagination, it sort of looked like the letter "Y" .
A later incident involving a girl I knew, and we're still 5ish years old, at the same daycare, went in to use the 'bathroom'.
But she decided (for whatever reason her young mind came up with), to use the urinal "like a boy". Me and the minder came in suddenly and saw her standing there, with her pants/panties around her ankles, her body arched way back (like she was doing the limbo), fingers spreading her labia wide open, so she could direct a stream of urine into the 'stand up toilet'. The female minder exclaimed "Venus, what are you doing"? (as if it wasn't obvious). Venus tried to explain why she felt the urge to stand to pee. I don't really recall her answer, because I was too busy inscribing the whole scene into my memory. I only recall it today, because it was so odd.
After that, I tried to engage the girls into play sessions of doctor, so I could get a closer look at those wonderfully simple looking female organs. So much comes from seemingly so little...