WALNUT CREEK, Calif. — At Forma Gym in Walnut Creek, Calif., 13-year-old Zakery Galambos climbs a newly installed bouldering wall with the help and encouragement of his personal trainer, Robert Jackson.

WALNUT CREEK, Calif. — At Forma Gym in Walnut Creek, Calif., 13-year-old Zakery Galambos climbs a newly installed bouldering wall with the help and encouragement of his personal trainer, Robert Jackson.

About 20 miles away at Hercules Fitness Gym, kids ages 3 and up work with personal trainers and CrossFit instructors Lesha Capitanich Kastl and Bryan Kastl on running and squatting skills as their parents take pictures.

Instead of being left at home or plopped into the child care center at the gym, kids as young as 3 are learning some of the same exercises — modified for their ages — their parents are doing. They are working with personal trainers, taking yoga, Zumba, boot camp and CrossFit classes.

"Parents want their kids to be introduced to a gym and have the tools for exercising later on," says Jackson, co-owner of Forma. His gym has about 50 young clients, ages 6 and up, whose parents pay up to $75 an hour for these one-on-one sessions.

With nearly 20 percent of children obese or at risk of becoming obese, according to the 2008 Centers for Disease Control and Prevention Pediatric Nutrition Surveillance System, many parents are desperate to get their kids active.

But there are other reasons, besides weight management, why parents are footing the bill for professional fitness services. Kids like Zakery, who plays ice hockey, want a competitive edge over their peers.

"We're giving him all the tools he needs to succeed," says Nelson Galambos, Zakery's dad. "Not only does it keep him busy and out of trouble, he excels. It's a wise investment."

Galambos says it will pay off for Zakery not only physically but mentally.

"He will notice a difference when he competes against kids his age and older kids," he says.

Zakery asked for a trainer, and Galambos says that he wouldn't push Zakery to use one to improve his hockey skills if Zakery didn't want it. The family hopes the extra help might lead to a scholarship for Zakery, who would like to attend a top-tier school on the East Coast such as Boston University.

Others, including 17-year-old Matthew Haupmann, work out with personal trainers to boost their self-esteem and improve their physiques. Haupmann has been working with trainer Kirk Michals for more than a year. A skinny kid when he first arrived at All In One Fitness in Walnut Creek, Haupmann has gained 32 pounds of muscle.

"I feel a lot more confident now that I have a bigger body and more muscle," says Haupmann, adding that the exercise has helped him focus in life in general.

His trainer, Michals, sees the change in Haupmann's personality.

"When kids train, they become more open when they become more active. Matthew has really opened up a lot. If he didn't find this, he might have not found an outlet," Michals says.

His mom, Emma Andreoli, says Haupmann was never into sports so she wanted to get him active somehow. Having him come to All in One Fitness has helped Haupmann find his exercise niche. She thinks he will enjoy exercising like this for the rest of his life, and now Haupmann is training with Michals to get fit in order to become a firefighter.

"He's found something (working with a trainer) that he likes, and it's worth it to me," she says.

Back in Hercules, eight young children surround Kastl and her husband during the CrossFit class. CrossFit — a cross-training program developed for adults but tweaked for these children — has the kids running around, using suspended rings and playing games for 30 minutes.

Three-year-old Sierra Thompson is engaged in the activities, although she likely doesn't even know she's exercising. She does squats before her turn at duck, duck, goose and keeps up with the older kids as they run around the workout area.

Sierra's mom, Staci Thompson, used to teach physical education at a local school. She's worried about current obesity rates for children and adults as well as cuts to physical education classes at schools.

"I think it's important to get kids exercising at an early age," she says. "I want Sierra to have a healthy lifestyle and be healthy."

Carol Jorgensen, guardian to 4-year-old Khamani McGhee, says she models fitness for him by working out herself at Hercules Fitness Gym. Experts say parents and guardians are the best role models for their children's future habits, and little guys like Khamani will learn that exercise is fun through classes like CrossFit.

And classes, training and gym time are considered safer in some parents' minds than letting kids play outside. Thompson noted that when she was a child, she used to play with friends outside, leaving the door unlocked all day. Now, she says, "I lock the door right when I go inside. It's just not the same as it used to be out there."

Kastl agrees. If kids don't have a place to go play and get exercise outside or in a gym, they'll likely stay sedentary at home playing video games.

"We lived in a cul-de-sac and played all day. You just don't see that anymore," Kastl says.

Training kids and catering to kids in exercise classes is different from training adults. Kids' bodies are different — they are still growing and do not yet have all the muscle mass they will have as adults — so exercise has to be modified for their specific needs. For instance, in Zumba classes for children, the moves are toned down and the pace is not as frenetic. And in yoga, instructors use different names for poses and hold the kids' attention through storytelling.

Lynn Love, a personal trainer at Club One Silver Creek in San Jose, says kids are generally shy when they first arrive at the gym and are surrounded by adults.

"Most of them, when they come into the gym, are very uncomfortable in there because they don't know what to do, and they don't even know what they are looking at (in terms of exercise tools)," she says. "Even adults are uncomfortable in a gym because they don't know what to do."

Love, who says she looks like a 16-year-old herself and is therefore approachable to a younger age group, says teaching kids how to use everything correctly puts them at ease in the gym. She helps them find their target heart rate and ideal weight for their age and height.

Jasmine Buczek, co-owner of All in One Fitness, says kids are also up for new challenges when they train and are often more excited when they see the results of their work.

"With adults, they want to see results quick, and they tend to talk down on themselves, especially women," Buczek says. "Overall, adults have a harder time noticing the positive results. They are harder on themselves. Kids can be very appreciative very fast when they see just a little bit of results."

Fortunately, Buczek says, no matter what sort of exercise routine a child excels at, time is on the side of the younger set. Kids have had less time to build up bad habits than adults who have spent many years being inactive and eating poorly. Buczek teaches nutrition tips as well as physical exercise.

After a few boxing exercises at Forma Gym, Zakery takes a break for water before plunging back into weights and coordination exercises. He says working with Jackson will certainly help his game.

"I am building strength so I don't get pushed around," he says.