Anyway, I wanted to say that I wouldn't hesitate to bring my kids if they wanted to go. I'd explain that people don't waer their clothes at this place, but that it was fun and they were welcome to come along if they wanted.
Now, I grew up in Japan (after age 10), and spend many evening at the hot baths there, and some were co-ed. When I was first invited, I declined, out of embarrassment, but all my friends went with their families... After awhile, I got curious, and started going. It's not a big deal. It's common there to go, even if you're just staying the night a friend's house. About 8 o'clock, everyone ups and goes to the hot bath, where you shower and then soak in nice hot baths together. When I was in high school, I even once had a slumber party where we all went to the hot baths together.
Nude recreation (and bathing) together is not new, and it's not wierd.