Imagine two buff drillmasters in tight, black T-shirts barking commands at a group of 8-year-olds running on adult treadmills or tossing around 6-pound medicine balls. Is this someone’s satirical vision of a fat-phobic future? Or is it the horrific imagined outcome of the current fitness craze? In fact, this exact scene plays out every Tuesday and Thursday at 4 p.m. at Hanson Fitness (826 Broadway, 212-982-2233, www.hansonfitness.com), near Union Square, where a small crew of sweaty youngsters, far from frightened, giggle continuously as owner Harry Hanson and an assistant take them through a miniaturized 45-minute circuit-training routine.

“You’re not going to stunt your growth by doing push-ups,” said Mr. Hanson in defense of his adoption of adult strength training methods – calisthenics,cardio,and ju-jitsu – for preteens. “We’re personal trainers.We’re good at helping people get into shape. If you have a kid who’s overweight, we can help.” High-profile clients have included talk show host Ricki Lake as well as her son Milo.

Hanson Fitness’s $25 a class Camp Kids and its more aerobic counterpart, Cardio Kids, are just two exercise programs for children to appear on Manhattan’s gym scene recently. Programs at the sports multiplex Chelsea Piers (23rd St. and Hudson River Park, 212-336-6500, www.chelseapiers.com) and the New York Health & Racquet Club’s northernmost Upper East Side facility (1433 York Ave., 212-737-6666, www.nyhrc.com) have also expanded youth fitness options beyond the commonplace choices of competitive sports, wrestling, and dance.

“We have 2,000 kids a week who take classes. We know what kids like,” said Peter Kormann, the assistant general manager who helms all of Chelsea Piers’ youth exercise programs outside of basketball and soccer.

“Parents are looking at their kids and seeing way too much video games, way too much TV, probably too much eating,” he said. “The type of child I want is the one who in two years is going to have a problem,” he added, referring to the weight gain caused by lack of physical activity that is made worse by poor nutrition.

Mr. Kormann, a former Olympian, hopes to prevent that by building a bridge for children to athletics and initiating a lifelong commitment to physical well-being. “The 5 to 12 age group,” he said, “that’s when lifelong patterns are formed.”

This past Saturday, Mr. Kormann and his staff began offering 17-week Fun Fit courses ($540-$995) that teach,among other things,the basics of weightlifting to youngsters ages 5 through 12. Each 90-minute class, in contrast to Mr. Hanson’s, uses resistance-training machines reproportioned for smaller bodies.

“We’re the first place in the country that has this equipment,” boasted Mr. Kormann of the Italian-imported line from Panatta Sport. But the military press, the lat pull-down, and the cardio bikes are more than scaled-down replicas of their grown-up equivalents. Their bright primary colors and space-age designs seem suitable for a Hello Kitty gymnasium, while their illuminated monitors (which guide the pace of each repetition) and flashing lights (which go off when form goes awry) add a playfully high-tech touch. Since weights max out at 25 pounds, Mr. Korman said there’s “not a lot of building but a lot of muscle toning.”

“In Italy, they have these in the malls,” he said, “so parents can drop their kids off with a trainer while they shop.”

Whether doing three sets of 10 reps or cycling in place will hold a child’s interest for a whole shopping spree strikes personal trainer Larry Mischelli as unlikely, however.

Mr. Mischelli is the 20-year veteran instructor behind New York Health & Racquet Club’s Sport Fit Kids tween circuit-training program ($80-$120), which will launch February 3 and run every Thursday through March 24. He believes the main difference between coaching adults and children involves accommodating the latter’s shortened attention span. “You can’t stay with one activity too long,” he said. “You can’t keep their attention for more than five minutes.”

In order to keep wandering minds focused and restless bodies engaged, Mr. Mischelli’s program makes use of standard health club gadgetry such as dynabands, minitrampolines, and cardio steps, sports equipment like basketballs, footballs, and jump ropes, and even the occasional hula-hoop.The course is modeled after an after-school program he started in 2004 at nearby P.S. 158.

Sport Fit Kids, Camp Kids, and Fun Fit all keep class sizes small, with a maximum of 8 students. The reason behind the more personalized approach across the board is simple. New York Health & Racquet Club group fitness director Maryann Donner said,”We want them to fall in love with fitness at a young age.”

But just how young is constantly changing. Mr. Kormann, after all, is in the midst of developing a baby gym in which cushioned ramps will allow classes of “nonwalkers” to learn the rudiments of gymnastics.Already complete is a ball pit filled with blue foam pieces to simulate a lake and an adjoining wall-sized mural of the great outdoors. “It’s a grand concept formulated from a dream,” he beamed.