When I was very young, we bathed in the bathtub, and as I recall my mother supervised that. I think I was probably eight years old when my younger brother and I accompanied my dad to the shower in the basement, mostly to get instruction on how to take a shower. I dont recall being particularly intrigued by the nudity aspect. I probably had seen my dad nude changing to swim or such. We definitely werent nudists at home. My appreciation of nudity, solo and social, came later, but never associated with family.
In Finland we had a sauna in our house, so the whole fam would sauna and shower naked together every Friday. Even if I had friends around, they would join us, or if I went round my mates house on summer house, their dad would take us skinny dipping and sauna bathing. There were never swimwear involved. So I have showered with dad, uncles, brothers and friends dads. When bigger groups, the men and women would usually separate. Dad and grandads take sons, and mothers daughters. Often cause of socialising rather than anything else.