It is, indeed, a good reason, if you are looking for reasons!
I have a 4 year old (nearly 5) who has an irrational fear of public toilets - and any toilet with a ceiling fan - though she will go to our ensuite which has a ceiling fan with an electrical fault which doesn't work and never will - but only if someone is upstairs when its dark (though will in broad daylight) 
Child went 17 hours from Melbourne to Dubai without weeing (night flight so less urine production but still, please?)
So I suppose you might have a 6 year old who you have to take (I don't see her ever getting over this phobia, I expect I will have to go on honeymoon with her, I mean her honeymoon, as I have been married for about a thousand years). I shall clear my diary.
She doesn't come in with me though, but there may be reasons why one might, though I am struggling with them. I would have probably locked myself in and let them have a panic attack or 3000 in order to shit in peace, which is a basic human right. I would refer you to the Home Office homepage but I can't be arsed, but I'm pretty sure they have a link.