[dirtyroboto]

Not so much Onsen but my local sento....

Has loads of kids.

Now please understand that I am in the mens section and I see boys and girls come in with their fathers and never cause any problems, apart from shouting too much.

Due to the way Japanese do bathing there is always very little issue as many of the kids already know how to bathe from an early age.
I am sure that if you bathe with your daughter and she gets noisy then no one will care.

Lets face it, If she lets loose in her nappie then you be the first to know it and also the most embarresed person that day.