Playing outside is so five years ago. Now kids keep buff by pumping it up at kiddie gyms.

It may sound like a grown-up routine, but MSNBC reports many parents are enrolling their children in fitness centers or buying them child-sized workout equipment so they can stay fit.

But are little kids too young for the gym? Pediatrician Dr. Cara Natterson weighs in:

"By joining a gym, many children can get the exercise they need in a format that fits their lifestyle. I have seen tremendous benefit from gym-style workouts among children, as young as 5 or 6 through the teen years."

There are other perks, too. "Most gym-style workouts also offer lifestyle and nutrition teaching. It is great to get a child exercising, but it is just as important to teach that child how to make good choices throughout the day. Learning how to eat balanced meals or how to choose the stairs over the elevator takes teaching."

But Dr. Cara does have one word of warning: "Be careful to choose a gym that caters to children," she advises. "It is unsafe (and unfun) for a child to go to an adult gym, due to risk of injury."

What do you think of gyms for kids?

Dr. Cara Natterson, author of Your Toddler: Head To Toe, is a pediatrician and mother of 2. To buy a copy, click here. She is currently working on the forthcoming book entitled Dangerous or Safe?