"Are you bleeding, choking or on fire?"
I ask my kids this about once a week. This is the only response they will get from me when I am in the bathroom and their tiny little fists pound on the bathroom door. It doesn't matter if I am showering, putting in contacts or tinkling. These are the only situations that I allow to interrupt me.
I have had other mom friends lament the fact that they have not gone to the bathroom alone for nearly a decade because one of their children follow them in or weep inconsolably at the door. Their children just can't live without them for any amount of time.
I believe that the 23 1/2 other hours of non-bathroom time that I devote to my children assure them that I do indeed love them and are available to help, hug and listen. I don't believe any moderate crisis can be solved by my shouting through a wooden door and also believe that any minor skirmish can be successfully dealt with after a thorough washing of hands. Major catastrophes such like bleeding, choking and flames, however will be dealt with promptly.
Full disclosure - I have never been an open-door policy kind of gal. I still lock the bathroom door, even if I am home alone. I run the fan and water so nobody can hear me tinkle. If I am feeling particularly bold, I will skip the running water if I am home alone. Maybe.
Other families don't mind a little company in the bathroom. Good for you. My opinion is not a one-size fits all families type of edict.
But, if like me, you want a little time to yourself, take it. Your children will survive. It might be good to learn basic boundary issues so they don't rush into their boss's bathroom stall in a couple of decades.
From those who say it wouldn't work with their kids, I politely disagree. Bathroom locks were invented for a reason. And, with consistency, they will figure it out. They are smart kids. And, like my kids, they will stop knocking (or slink away when reminded of what constitutes a bathroom interrupting emergency).