Finns parents respect kids privacy please!

I don’t want to offend anyone, I simply want to understand some things. I know that going to the sauna with the family is something sacred to the Finns. But there is something that costs me a lot to understand and worries me. I know many Finnish teenager boys from different cities (Helsinki, Espoo, Vantaa, Rovaniemi, etc.) and they have told me that they go naked to the sauna with their parents, including mother. Why don’t mothers respect the privacy of their kids when they begin to hit puberty? In adolescence they could even get unwanted erections and mothers are going to be there looking at their kids penises! I think is disrespecfull. Could someone explain me better? Because it's something that confuses me. Regards!