A couple of weeks ago, DH had a business dinner, and I was running late getting the kids to bed, so I bathed them together. DD is 10 months and DS is 3. DS thought this was awesome and he asks to take a bath together almost every night. DH doesn't outright say no, but he doesn't like the idea. DS is often around when we bathe or change DD, so it's not like he's seeing her naked for the first time. At what age do you think a brother and sister sharing a bath is inappropriate?