While the industry is devising new ways to get children active, parents and fitness instructors should be mindful that a "workout" for a child is different from that of an adult.

"One common mistake that is made in the industry is that programs designed for kids treat them like they were mini-adults when they aren't, either mentally or physically," says Jonathan Ross, a personal training and fitness consultant in Washington and the American Council on Exercise's personal trainer of the year.

Many new equipment pieces being produced are just miniature versions of adult weight-training machines with straps and pads that only work one muscle at a time, Ross says. But training a child like an adult can lead to overload on still-developing nerves, bones and muscles.

"A child's bones, muscles and joints aren't capable of the intense resistance programs adults usually do," Ross says. "Their attention spans are shorter, and they are aren't naturally drawn to repetitive, consistent effort. Plus, the bulky equipment gets away from the natural randomness of the way kids move and are active."

Ross says a child can be trained at any age, as long as the program meets the unique physical and mental characteristics present in that stage of their development.

"Fitness is more of an adult concept," Ross adds. "Kids only know movement. They just go out and play and don't think about carving out a separate time in their day just for exercising. It has to be explained how to devote time to physical activity."

Here is a list of Ross' "dos and don'ts" regarding fitness programs for kids:

• If working with a trainer, a child has to be mature enough to follow instructions. A 3-year-old, for example, wouldn't do well in a class where his parent wasn't present to supervise and discipline.

• Stay away from heavier resistance training and concentrate on mostly free weights. Do activities such as squats, push-ups or lunges that work large muscle groups and require multijoint movement.

Train for skill first, strength next and then endurance. A high level of fun is a must and can be achieved by adding fitness toys, including balance disks and multicolored balls.

• Be careful with aerobic training because children have smaller hearts that have to beat much faster in order to get a benefit from the exercise. To benefit from traditional cardiovascular training, an exerciser needs to have 10 to 20 minutes of sustained activity. However, it's very difficult for a child to maintain that kind of intensity long enough to make aerobic training useful for them.

Instead of sustained aerobic activity, aim for games that involve running and stopping or chasing.

Take a look at Ross' "Family Fit Plan" at familyfitplan.com. His program is designed to get parents and kids playing together as a form a of exercise activity. It's structured enough to get results but not so controlled that it's no longer fun.

"Jogging doesn't make sense for a kid," Ross says. "Most kids can chase a ball or another person all day long, but to force them to run without having a purpose seems very counterintuitive to their brain."