Let the child decide is the mantra recited by health professionals to parents considering toilet training their babies, toddlers and young children. It is a mantra that can be traced to the 1960s and leading paediatrician T. Berry Brazelton, who was among the first to advise against the often-harsh toilet-training techniques of the pre-war years in favour of a gentler, child-led approach.
By the '70s, the message was that toilet training before a child was ready could cause psychological damage.
But this message is now being challenged by health professionals and parenting experts, such as author and childhood nurse Robin Barker. They say the philosophy of waiting until a child is ready, combined with the use of disposables, has meant children are staying in nappies longer.
''The average age of children being trained has slipped from two to 2½ to three or even four in the United States,'' Barker says.
While she does not promote a return to the draconian measures of the 1940s and '50s, she believes the pendulum for letting children decide has swung too far.
I have observed a window of opportunity between 18 months and two years where a lot of toddlers start to show an interest in the thing and that fizzles out.
''It would seem now that many parents are not really potty training their children,'' she says.
''They drift along and wait until the child is three or even four and hope they will come out of nappies in a couple of days.
''In effect, we have doubled the time that children are in nappies. There is also the feeling of, 'What does it matter, what the hell'. Our priorities have changed. We want kids to be talking Mandarin and playing the violin and they are still wobbling around in nappies.''
There has been little long-term research into toilet-training ages in Australia but research from the US and Europe shows that in the late '40s, toilet training was started at or before 18 months. By 2006, the age had risen to between 21 months and 36 months.
A 2003 American study found that only half the children on which the survey was based had completed daytime toilet training by the age of three.
Barker believes the convenience of disposable nappies means there is less incentive for parents to train their children. There is also less incentive for children to learn because disposables keep moisture away from the skin, meaning tots no longer know what it feels like to be wet.
In Australia, 95 per cent of nappies used are disposable, up from 40 per cent in 1993. With the average baby changed six to eight times a day, this represents about 3000 nappies for each child a year. In Australia, disposable ''pull-up'' nappies are now available for children 17 kilograms and over - the weight of an average four-year-old boy.
''The marketing techniques of disposable-nappy manufacturers have a lot to do with it. It doubles their profits to keep children in nappies for twice as long,'' Barker says.
Texas psychologist Dr Linda Sonna is among critics of Brazelton's approach in the US, where he has been the spokesman for disposable-nappy giant Pampers since the 1960s.
''The whole idea of waiting for a child to tell you they are ready comes from the disposable-diaper industry,'' Sonna says. ''The knowledge that it is even possible to train early has been completely wiped out.''
She says the best results are achieved when training starts before the age of two and in conjunction with cloth nappies. ''Cloth nappies mean children understand the sensation of being wet.''
Anna Christie also believes training should start well before two. She spent two years reviewing scientific literature about toilet training and interviewing Australian parents about their methods for her report, released by the University of NSW last year, Toilet Training of Infants and Children in Australia: 2010.
She says the key factor is not the readiness of the child but the expectations of the parents. ''We have replaced skills with products in many aspects of our life. Parents find it easier to put a disposable nappy on their child than to put the effort into training them.''
Paediatrician Chris Pearson, chairman of the child development and behaviour group with the Royal Australasian College of Physicians, agrees most children have a ''window'' when training is most easily achieved. He says that for girls, this is usually between two and 2½ and for boys, between 2½ and three.
''Children should be toilet trained as soon as possible. But it's important not to create emotional issues for the child by trying to force them to do something they are not ready to do,'' Pearson says.
''As soon as the first sign of emotional distress shows up in the child, it is time to stop and try a different technique. If you are creating distress, you are highly likely to inhibit the success of training. As long as the child is co-operative and parents are willing to make an effort, it doesn't matter what age they start.''
Pearson is also concerned with the use of pull-ups as a toilet-training aid. ''My instinct says they give implicit permission to pee themselves.''
Cathrine Fowler, a professor of childhood nursing at the University of Technology, Sydney, believes training before the age of two can be futile. Children need a level of mental and physical maturity to succeed, she says.
But Barker says waiting until a child is two can backfire, as it coincides with other developmental peaks, such as learning to say no.
''I have observed a window of opportunity between 18 months and two years where a lot of toddlers start to show an interest in the thing and that fizzles out,'' Barker says.
For her research project, Christie interviewed 53 primary caregivers about toilet training.
She found the age at which toilet training started was a major determinant of the age when training would be completed. The best results were for those who started training from 19 months to 24 months. On average, these children were out of nappies by 25 months.
Christie says that among the parents who waited until their child was between two and three, some trained quickly and others took much longer than those in the 19- to 24-month group because the training period coincided with the ''terrible twos'', when toddlers start to assert their will.
For most women around the world, toilet training starts from birth. While it was the child-centric parenting approaches of the '60s and '70s that relaxed the rules on toilet training in the West, a similar philosophy is now driving the nappy-free idea.
The promoters of what is commonly labelled ''elimination communication'' or ''EC'', say they are using the same methods as women around the world who cannot afford nappies. The process involves the parent watching the infant for signs, such as facial expressions, noises or squirming, and then ''holding them out'' - taking the child to a potty, sink or outside. When they successfully ''catch'' an elimination, the parent signals encouragement.
Advocates say not only does EC work, it is also a way of becoming closer to the child.
In 2006, Herald journalist James Woodford documented his experiences of practising EC with his fourth child. At first sceptical, he became a convert after watching his daughter eliminate on cue into the sink or toilet as early as two weeks of age. By nine months, Woodford wrote, he could ''count on one hand the number of times I have changed a dirty nappy''.
Bellingen parent Nicole Moore is among the advocates and has produced a how-to DVD for parents.
As with other techniques, Moore says the results for when children are trained varies. Some are trained by 12 months, others take a little longer.
''I use the word 'gentle' at least 10 times in the DVD - it is a gentle process,'' she says. ''Being nappy-free gives you the freedom to choose; it is not about being out of nappies all the time but it doesn't mean you are locked into being in them all the time either. For the child, it means not having to go back at age two or three and re-learning something.''
Moore admits the practice works best with other attachment parenting techniques, such as carrying your baby in a sling or co-sleeping. ''When you're wearing your baby, these are symptoms that are impossible to miss. If they are five metres away on a rug, it is a lot harder.''
Mainstream health professionals are yet to back this method.
''Asian and other cultures have been holding their children out forever,'' Fowler says. ''There, it is the parents who are being trained to read their baby's cues. There is probably some behavioural effect on the child but the only person who is trained is the parent.'' Barker says parents who want to try nappy-free methods from birth must be dedicated but adds it is something all parents can do to some extent.
''When I did my training, I was taught that training children from birth was wrong … But in my work, I would see people from China who would train from a young age and have their babies all trained by 14 months and it wasn't causing much of a problem at all.''
Do you think parents are leaving toilet training too late? Join the conversation on the Essential Baby Forums.