Read about parents potty training babies here: Parents begin potty training at birth.
It reminds me of what my parents did to me when I was still a baby (younger than one year old). I don't know when exactly my Mom started potty training me, but it was obviously when I was pretty young. Back then (I was born in 1978) in Indo there were no disposable diapers and most mothers were still work-at-home mothers, so they started potty training their babies early on.
Well, during the nights when my Mom detected that I got anxious and I kept on moving around in my crib, she'd wake up and wake me up and potty train me. She said that parents could detect when their babies wanted to poo or pee.
Anyway, after some time Dad reprimanded Mom for waking me up every night to pee or poo. My Mom was seething inside, so one night when she heard me moving around anxiously in my crib, she didn't do anything. A while later, Dad woke up himself and found out that I had peed and I got pretty wet all over (I guess I must've peed a lot), so Dad had to change everything I was wearing. He did that while cooing, "Oh dear girl, look at this mess. You're really wet, honey."
Mom was laughing inside. She said to herself, "Even though you think it's cruel to wake the baby up in the middle of the night to poo or pee, it is by far more practical than having to change everything, you know?" But she said nothing to Dad.
The next night, when my Dad heard me moving around in my crib, it was he himself who woke me up to potty train me. LOL!!! Mom loves telling me stories about my childhood and this one always makes me SMILE. ^_______________________________^