A group of Vietnamese mothers were able to potty train their children at just 9 months old, according to a 2012 study from the University of Gothenburg in Sweden. They key? They used their own vocal sounds coupled with a reward to help the babies understand when they were supposed to "go to the bathroom."
This technique, which may be used in other Asian countries such as China, uses a conditioning technique that includes a signal, the whistling noise, to prompt the baby. Depending on the result, he or she receives a reward in the form of affection and praise. In most western countries, babies are potty trained much longer, and on average infants need diapers until about three years of age.