Ever!
It's impossible, though. You're forced to witness the most intimate functions of your children's bodies; inevitably, you find yourself discussing it with your partner, your mother, the neighbors, etc. I've never liked it, but I accept that it happens.
I don't quite understand people who are interested in it just because. Like my friend's sister, who picked Diddly up, stuck her nose in his rear and gleefully announced, "Someone did a stinky!"
A stinky?
Understanding that you might succumb to this unsavory terminology as a parent might actually be good birth control.
Children, of course, like to talk about what comes out of their bottoms. I watched my friend's four-year-old for a few hours the other day. Within five minutes of being at my house, she told me what poop is ("food your body doesn't need"), what she'd eaten that morning ("pancakes"), and what her poop had looked like ("a big snail").
Co-workers, too, like to talk about poop; specifically their inability to do it in a public stall.
It's unavoidable.
But oh my gawd, do we really need an app to track it?

One that records the details of what comes out?

One that reassures you that if you find a "surprise" you can email the details to your doctor? (The app makers—Similac—don't say what they mean by surprise. I'm guessing they don't mean something fun like a leprechaun or a nip of vodka. I'm guessing they mean something really troublesome, like a receipt for lingerie that you never got or a neighbor's pet.)
Why isn't there an app for vomit? That also comes out of children's bodies and often indicates a health problem. Green poop? Maybe. Green vomit? Yes, especially if there are surprises in it too.
To finish off this poop extravaganza, I'd like to leave you with the one commercial that makes me cringe with embarrassment for the human race. Whenever this commercial comes on I picture a living room full of five-year-old boys bursting with juvenile excitement over this masterpiece of potty humor.
Or dads.
Aren't you glad you stopped by today? I sure am.