Originally Posted by
LapLap
Separate gender baths don't have to be separate for a child not old enough to look after herself for an hour.
If she's that young, she can accompany you both.
My own kid is 6, never been an issue for us, she decides who she'll bathe with - Mum (me), or Dad, or Granddad.
Resort places (like those in the Hoshinoya or Century Hotel chains) will usually have a children's area close to the restaurant and onsen. She goes there if she wants a shorter dining or bathing experience.
When I lived in Japan, I went to the public bath, and although there were separate men's and women's sections, there was a door about a meter high between the two sections, and both little boys and little girls used it to move freely between the sections. There was a sign on the wall that said that children over the age of 8 were forbidden in the area assigned to the opposite sex.