The founder and research director of the programme, Paul Sacher, said many parents of bigger children did not realise their child was above the healthy weight range, or put it down to "puppy fat" that would disappear.
"However, being overweight or obese as a child is a serious condition. Overweight children suffer physically and emotionally and it can lead to serious health problems in later life," he said.
"Mend programmes help boost children's self-esteem while changing the way everyone in the family thinks about what they eat and being active.
"Children and parents also meet others who are in a very similar position so they form their own supportive network."
Families taking part in a trial lost an average 4.3cm (1.7in) from their waists after six months.
Courses will be run all over Wales in selected areas and more information about healthy living will be made available to families unable to take part.
Hundreds of health professionals across Wales will also receive awareness training and tips on how to support families with obese children.
AREAS COVERED BY COURSES
Neath Port Talbot
Vale of Glamorgan
Rhondda Cynon Taf
Last week, an NHS dietician said children as young as two were being treated for obesity.
Dr David Haslam, clinical director of the National Obesity Forum, said he welcomed any scheme to tackle obesity but questioned whether it was targeting young enough children.
He said: "It's important to catch them early. The crucial time is the first five years. £1.4m is a drop in the ocean and is nowhere near enough money."
Conservative health spokesperson, Jonathan Morgan AM, said: "While we welcome any investment in tackling this health time bomb we have to think seriously about how money is spent.
"Sending people on 10-week boot camps will not in itself tackle the long-term problems caused by obesity.
"We need a co-ordinated strategy tackling the way people see food, and one that also ensures young people see exercise as a normal part of their daily routine."
Peter Black AM, Lib Dem health spokesperson, said while his party welcomed any initiative to help overweight and obese children in Wales, questions needed to be asked about why Welsh children were "comparatively more overweight by international standards".
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