They also aim for sinks, bathtubs, trees, bushes and tires.
Letting the baby go to the bathroom in anything other than his or her pants will do, according to the rules of "elimination communication," as going diaper-free is called by the parents who practice it.
The idea is to recognize the baby's need to go and then communicate to the baby when he can do his business by holding him over a toilet (or something) and making a sound. Parents choose the method for many reasons, including fostering better early communication with their children and reducing their environmental impact by getting rid of disposable diapers.
"It's not potty training," said Tami Colon, 36, a preschool owner and mother of two diaper-free children in San Jose, Calif. "It's not coercive. It's really just responding to the needs of your baby."
She said she tries to watch for signs her children need to do their business. When they make a certain noise or a certain face, she will carry them to a potty (or something else) and make a soft hissing noise to let them know it's O.K. to go.
Most diaper-free moms aren't diaper-free at all, said Jenay Burke, 33, who started her company, Naturally Diaper Free, shortly after trying the method for her second child in 2011. She makes cloth diapers, split crotch pants and other items out of her home in Portland, Ore.
"The common misconception with EC is that you don't ever use a diaper, you have a naked baby all the time, you're constantly covered in pee and poop, and your house is a mess," Burke said. "It's not like that."
She said families use cloth diapers as a backup for when they don't "catch" the baby's business in some kind of receptacle. (The cloth diapers make it easier for moms to tell when babies are wet than absorbent disposable diapers.) In that case, it's a "miss," but they don't reprimand babies for it.
"As long as there's no scolding done, which I would certainly not be in support of," said Dr. Julie G. Capiola, pediatrician at NYU Langone. "I don't think the child feels any pressure with the parenting style."
The practice drastically reduces the occurrence of diaper rash because the child is rarely sitting in a wet diaper, Capiola said, but fewer than five families have asked her about it during her career. For most of them, it's not practical unless a parent stays at home during the day, she said.
For Burke, communicating with her children nonverbally about when they needed to go to the bathroom gave her a sense of empowerment when she was a new mom and felt she had no idea what she was doing.
When Rebecca Hiebert, 33, had her second child, she decided to try the diaper-free method after initially being skeptical. If her baby couldn't hold up his own head, how could he control when he peed or pooped?
So when her son was four days old, she held him over a toilet. To her surprise, he peed.
Four days later, after a trip kept the family away from home for longer than expected, Hiebert assumed her newborn would have gone in his diaper. As soon as they got to their home in Steibach, Canada, she found that the diaper was dry and held him over the potty. He went.
"They know the feeling just like they know the feeling of being hungry," she said. "It's just not well known in our society."
Capiola said most children can't control their bowels or bladders until they're about 2 years old, but they usually potty train after they're a little over 3 years old.
Diaper-free moms say their experiences have taught them otherwise.
Colon said her son was 4 months old when he sat on his grandmother's lap in a library as they read a book about the alphabet. As they turned the pages, they made a sound for each letter.
When they got to "S," he peed.