The director of SureSlim New Zealand, Phil Pullin, knew of at least one 9-year-old who had come to its Pukekohe clinic with a weight problem.
Unlike weight-loss programmes Jenny Craig and Weight Watchers, lifestyle programme SureSlim has plans for children as young as 6, but most of its youngest members were in their teens.
He said weight problems among children was an increasing trend.
"In your suburban schools today parents are too busy to make kids lunch, so they get money for a pie and chips. They don't do any exercise for a whole raft of reasons like people are a bit scared of letting their kids walk home.
"And then they go home and play on the computer. It's just a whole lifestyle change."
Fight the Obesity Epidemic spokeswoman Dr Robyn Toomath said figures showed almost 30 per cent of 2- to 14-year-olds had a weight problem in 2007, with 8 per cent obese.
She said children joining weight-loss programmes was nothing to do with fashion-conscious mothers concerned with their child's image.
"There's masses of data to show that it's much more the other way, that individuals don't think they're overweight when they are, and parents don't think their kids are overweight when they are.
"It's much more that we don't appreciate the extent of obesity."
Dr Toomath said it did not surprise her young children were being enrolled in weight-loss programmes but she was skeptical about their success.
"The data shows adult weight reduction strategies which involve dieting programmes are basically a waste of time and money and my suspicion is they are similarly unhelpful for children."
She said instead of asking people to lose weight she emphasised balanced nutrition including increased physical activity and a healthy diet.
Weight Watchers programme and delivery director Martha Lourey-Bird said weight loss was rarely recommended for children under 7 and adult-based weight loss programmes were not appropriate for most kids.
"It's more about guiding them towards increased physical activity and lifestyle change rather than dietary restrictions," she said.
"In cases where a child is in need of a weight-loss programme, Weight Watchers requires children between the ages of 10 and 16 to have a parent's signature and a doctor's referral with a goal weight range before they can enrol in the programme."
Jenny Craig New Zealand and Australia managing director Amy Smith said both nations faced alarming statistics about the future health of the younger generation.
"But this isn't an issue weight-loss companies can solve alone. It needs the engagement of government health departments, health-care professionals including dietitians and psychologists, schools, families and of course, parents."
- Natalie Akoorie of the NZ Herald