Whether a boy and girl can bathe together often depends on their age and comfort levels.
According to anecdotal information, the decision to allow a boy and girl to bathe together is often based on the specific children involved. As noted, if "they don't make a big deal out of it then no need to separate them until they get uncomfortable or feel awkward." In the example given, siblings stopped bathing together when the daughter was 4 and the son was 6/7.
