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Children as young as 7 are trading toys for treadmills and Barbies for barbells, clocking up hours with their own personal trainers.

Only in America, right? Wrong.

More Kiwi parents are spending thousands on expensive one-on-one fitness sessions for their children, industry experts told the Herald on Sunday.

They are either desperate to banish extra weight and the threat of obesity-related disease, or they want their child to excel at sport.

Auckland gym chain Club Physical has 69 children under 14 registered for training, and 774 teenagers aged 14-19.

Les Mills personal training manager Rob Richards agreed some parents were hiring trainers for "obesity and aesthetic reasons" while others wanted to make the most of their child's athletic ability.

"It's not as common as in the States, but demand is increasing."

Some parents believed if they invested money and effort when a child was young, they would reap financial rewards through professional sporting careers, he said. Think Tiger Woods and the Williams sisters.

But, he said, parents were not necessarily pushing their children. "Kids with a natural talent often want to do it."

Priced at between $40 and $80 a session, a personal trainer is not the the cheapest way for parents to maintain children's fitness levels. But for some, it's a last resort.

North Shore's Sylvestre Gahungu started his 13-year-old daughter with a personal trainer six weeks ago. He hoped regular gym sessions would save her from obesity-related illness, as well as teasing.

"She's been overweight since she was 5," he said. "We've always tried to get her into exercise and put her on diets, but it didn't work."

The girl's doctor said she was at high risk of developing diabetes unless she lost weight.

"We thought maybe the gym, and a trainer, could work as a motivator," Gahungu said.

"It's quite expensive but we look at what we can do that is best for her and so we are prepared to make some sacrifices." His daughter had lost 4kg since starting with her trainer. She attends the gym, with her mother, six days a week.

Brahm Richards is a 10-year-old fitness freak - perhaps unsurprisingly, because his parents own a gym. He's in two representative level soccer teams, plays tennis and takes karate, judo, wrestling and swimming lessons.

The Auckland schoolboy recently added time with a personal trainer to his after-school activity list.

"I want to play for the New Zealand Knights," he told the Herald on Sunday.

Brahm said he hoped the training would help get him there. Dad Paul Richards, owner of the Club Physical gyms, said he hoped so, too.

Training children was controversial, he said, but becoming more accepted within the New Zealand industry and with Kiwi parents. "We're on the crest of a wave."

He said that even two to three years ago many trainers believed children and weights didn't mix. But US research, showed it was safe for children as young as 7 to use weights, with the correct technique.

Brahm's trainer, Toni King, 65, has nine children on his books. He provides nutritional and lifestyle advice for parents and children, on top of their regular workouts.

Personal trainer Jon Routhan has trained children as young as 8, but is now concentrating on group work with some even younger.

"I believe in getting in there as young as possible."

He is training 3- and 4-year-olds at a Ponsonby preschool, in a group exercise programme he developed, called Little Pinnacles. He said parents who hired trainers to get their children or teenagers off the couch often acted too late. Psychologist Sara Chatwin said parents should think twice before hiring a personal trainer. There was a fine line between healthy encouragement and pressure. Children could become hyper-sensitive to their image or weight, she said, which could develop into resentment or even anorexia.