We only have 2 boy's but I was a little girl we moved across country a few times and I always
had to ride with my mom, never could ride with my dad, although my brother had his choice on which vehicle he rode in.... wasn't until I was grown, out of the house and married that I thought to ask my mom WHY and she gave me an answer, when I was little it was just the way it was, I rode with mom, brother could choose, no questions asked... well duh, the 'reason' was that they did not feel comfortable with dad taking me to the bathrooms along the highway/interstate/rest areas. Simple. Had I of been old enough back then for them to explain and for me to understand I might have been a little less sullen riding in the car with my mom. In town and local I went lots of places just with my dad and I don't remember ever going to a men's room with him, might have, but probably not. I don't know how he handled the situation... maybe he waited until someone came out or asked a female to check to see if there was anyone in the bathroom, if it was empty he might of came in or stood at the door "warning" women that there was a "man" in their bathroom or a little girl in there alone and could they please until she came out before entering.
I have done the wait and ask (or watch) in a restaraunt until no guys were in the men's room so that my older son (age 5) who sometimes insists
that he go in alone, be completly alone in the bathroom and I stand guard at the main door on the outside blocking anyone new going in, not that I have ever had to stop anyone from entering yet... don't know really what I would say if they needed to go in ... can you hold it for a minute until my son finishes, just in case you might harm him while you are alone with him in that room....
For now I'm comfortable with taking them into multi stall women's rooms with me, I do try and pick the large stall so both can stand with me and I usually have one hold my purse and the other to hold something that I just took out of my purse so that they don't touch doors and trashcans. If it is occupied, I will either wait or have them hold hands and "hold the door" closed for me. I dont know at what age I will feel truely comfortable with them going into a extremely public restroom like at a reststop or a service station.
I don't know... as a female I wouldn't find it weird at all to be asked by a man if the bathroom was empty as I was leaving or to ask what the bathroom set-up was/ single stall or multiple in the women's room so that he could stand guard and block anyone new from enetering while his daughter used the bathroom alone. We don't go very many places that have long long lines to the bathrooms so maybe in a situation like that where there are tons of people waiting to go, that would not work well.