Here, in Eastern Europe, decades ago, especially during our communist era but also in the first decade after 1989, on our seaside at The Black Sea coast, it was a common practice for parents lo let their small kids to sunbath nude on our beaches. Not nudist beaches (we never had an official one) or clothing optional ones - just usual beaches.
During The '80s, in my childhood, I had also this "privilege" along with my siblings or younger relatives.
Usual, almost all preschool kids was seen nude on beaches, but was nothing uncommon at all to see even older children up to ages around 10 or so running around naked on the beach or even walking "au naturel" around the beach proximity.
In my case, I can say that I still remember me being around 4 years old and questioned my mother about the visual difference between boys and girls, so I'm pretty sure that this was the first time when I sow /noticed a girl vagina.
Another time, also being on the beach, but a bit older - possible when I was 9 - I remember that I started a one-summer friendship with a girl around my age who was accommodated with her family on the same hotel like us and also walked on the same beach area. One day, during this vacation, I remember that I sneaked up with that girl in a beach changing cabin and I asked her to drop her bottoms (she was always topless on the beach, wearing just the bottom part from a two-piece swimsuit, while I was still completely nude at 9). First, she hesitated, but after a few seconds she was agree that it was fair enough to be seen naked for a few minutes in a cabin while I was nude all day long on the beach. With this occasion, we started to play "the doctor" and I had the chance to have the first closer look of a vagina.