American parents now toilet train their children nearly a year later than in the 1940s, creating a massive sales boom for diaper companies. In 1944, Mayo Clinic doctors tracked 336 Rochester babies and found that 80% of parents successfully toilet trained their children by their first birthday. Today, the average age for starting training is 21 months, with nearly half of children not finishing until after 36 months.

This shift coincided with the rise of disposable diapers, which began with Marion Donovan's 1949 invention of the Boater. After manufacturers rejected her waterproof diaper cover, Donovan sold her patent for $1 million to Kennedy Company. Procter & Gamble later developed Pampers in the 1960s, reducing costs from 10 cents to 6 cents per diaper and capturing 80-90% market share by the early 1970s. The convenience of disposables fundamentally changed parenting norms.

Pediatrician T. Berry Brazelton's 'child-oriented' approach to toilet training, published in 1962, advised waiting until children showed readiness around age two. His philosophy, combined with disposable diaper convenience, pushed training ages upward. While Brazelton claimed his method reduced bedwetting and constipation, critics note that extended diaper use has created a multi-billion dollar industry that profits from delayed training, even as environmentalists raise concerns about landfill waste.