In the 60s, most American and European children were toilet-trained by around 18 months. And that was considered a long time, by earlier standards.
A 1935 U.S. Children's Bureau publication said toilet training should "always begin by the third month and be completed by the eighth month."
By 1997, according to a University of Pennsylvania School of Medicine study, only 4 percent of children were trained by age 2, with 60 percent trained by 3 years and 98 percent out of diapers by their fourth birthday. Today's new size 6 diaper fits children 35 pounds and over.
So what is the "right" age to train children?
Mainstream thinking, reflected in an article in the June edition of Pediatrics, the journal of the American Academy of Pediatrics, states that there is no right age but "in general, starting before age 2 is not recommended." Harvard paediatrics professor T. Berry Brazelton is a proponent of this view.
He is opposed by experts such as psychologist John Rosemond who supports a return to earlier training, because 3-year-olds in diapers causes too much stress on families, problems for some children, and conflicts with preschool workers. Rosemond's attitude harks back to N.H. Azrin and R.M. Foxx's 1974 book "Toilet Training in Less Than a Day."
Just how much is cultural and how much is physical is a big question in an era when grandmothers have been replaced by books.
Mark Stein, chairman of paediatric psychology at George Washington University, says, "I worked at a migrant preschool, and they didn't even have potty training. The kids just knew how to do it, probably from living so closely with other family members."