Early to the gym.(health centers offer a way out of child obesity)

Byline: Lini S. Kadaba

Gripping handlebars, Nick Piro positions his legs against a metal plate and pushes _ back and forth, back and forth.

A dozen reps later, he dashes from the seated leg press to the shoulder press, the next stop on his circuit of resistance-training machines. His goal is "to get a workout, to get strong," he says, without breaking stride.

Nick isn't a flabby cubicle drone hitting the gym to make good on a New Year's resolution.

At 6 years old, the trim first-grader and his two brothers, age 8 and 11, are regulars at the Swedesboro, N.J., Fitwize 4 Kids _ a growing breed of health clubs that cater exclusively to the pint-size set.

Correction: With juvenile obesity an epidemic nationwide, that would be the pint- and quart-size set.

Open since March, the club offers 6- to 15-year-olds of all shapes and sizes Curves-style circuit training, Weight Watchers-type nutrition classes, and incentive gifts (footballs, diaries) for continued attendance. Membership is $50 a month.

"We're not just an activity, like a karate studio," said Warren Gendel, founder of the California-based Fitwize franchise, which has expanded to 15 locations in the United States and Australia since 2004 and plans to add…