"I can do that," said 3-year-old Calvin Peters of Portsmouth as he scampered across the wooden floor sitting on a small blue scooter. "This is nice."

"I want to do it too," chimed in Jack Field of Newburyport, Mass., who is almost 3 years old, as he rushed to try out scooter tag with the others in the one-hour Rumble Tumble gym class in Portsmouth. "Me too."

In fact, it is true that as soon as most children — ages 16 months to about nine — enter the Rumble Tumble gym in Portsmouth, with its brightly colored indoor play zone, tumbling area and enclosed trampoline, their first inclination is to play.

"One of my goals really was when kids look at the place they would say, 'Wow, I'm not going to stop until I go there,'" said Amber Wyman, who together with husband, John, started up Rumble Tumble in downtown Portsmouth in 2005. "The intent was to create a 'wow' factor for kids."

And, for the parents, the gym with its classes, open gym time, slides, mats, extensive climbing equipment and trampoline, is a welcome outlet for their young children's energy.

"It's active and it's physical," said Erin Pompeo of Stratham, whose 2-year-old Arianna was a Rumble Tumble class participant on this day and whose 3½-year-old son, Anthony, also attends gym classes. "In the winter there's not a lot going on."

In fact, Ashlie Peters, whose family has a membership to Rumble Tumble, said her kids — 4-year-old Paloma and 1-year-old Nolan, as well as Calvin — come by at least a few times a week either for classes or open gym time.

"When you can't go to the park," she said, "they need something to do."

Jason Field, father of Jack and another younger toddler, echoed that sentiment, saying the gym is a welcome choice for his young family.

"You have to have these extracurricular activities for the children to be able to look forward to go to, rather than being stuck inside all winter long," he said.

But Pompeo said another plus is that the classes "pull everything together." As she put it, "It's fun school. Anthony learned his ABC's here before he learned them in preschool."

That is intentional.

Wyman started up the gym so she could have her own business, allowing some flexibility while juggling a home life including three children — 9-year-old Abby, 7-year-old John and 5-year-old Juliana.

"I really wanted to go back to working with children," she said.

"A teacher by trade," Wyman has incorporated elements like nursery rhymes, counting, colors and ABC's with the singing, socializing and exercising.

"We do consciously put those elements into our classes," she said. "We include counting, ABC's, traditional finger plays and traditional nursery rhymes."

For instance, class instructor Donna Polychronis begins the session with a book about drumming. As the children hear instructions about drumming, they take turns on small white and brown drums.

Quickly the preschoolers next move to propelling themselves on scooters so they can "touch the blue wall," before following and tagging Polychronis.

And don't forget the exercise.

Next up — tumbling on mats, sliding down small slides and walking across a balance beam just inches from the ground.

Peters said since her son Calvin has been coming to the kids' gym she has even noticed an improvement in his upper body strength.

"In the last few months he's learned to do things he wasn't able to do before," she said.

For instance, during the class, he hung by his hands from the rings — with Polychronis' support — while sticking his feet inside the rings as well.

"I love that he gets some energy out," said Jodi Field, Jack's mother. "Plus he's going to school next year so it's good for him to start with some discipline and waiting his turn with someone else besides his parents."

Certainly during the one-hour Rumble Tumble class, parents stand at the ready to offer back-up when a child temporarily becomes disinterested in following directions.

But Polychronis and the other instructors are trained to work with the short attention spans of small children.

No sooner do the children settle on a long stuffed caterpillar waiting their turn — usually — to hang on the rings, then they are walking on their hands and knees like cats and dogs to take turns on a small enclosed trampoline.

"You've got to keep them busy, keep them safe and keep them happy but you want them to accomplish something too," Polychronis said. "So if you can accomplish 60 percent of what you want you're doing really good."

In addition to public play, or open gym, time, Rumble Tumble offers classes like Monkey Business for parents and tots; Rumble Tumble for preschoolers; Play, Paint and Create for preschoolers; Sports Challenge and after-school programs such as Bounce on the trampoline, Jump Rope Jive and Cheer Gym. The gym also hosts birthday parties.

Despite a primary reliance on "word-of-mouth" advertising, families and children already come from as far away as Northwood, southern Maine and Massachusetts, Wyman said.

"I always say there's a lot of good energy in there," she said. "It's a very happy place."

Calvin, Jack and their peers wouldn't argue with that.