From teeny tuxedos to miniature munchies, there's a plethora of child-sized options for just about everything—except, according to St. Louis native Tracey Johnston, high-quality activewear. With her new web start-up, Kickety Split, Johnston is working to fill that void.

To understand why Johnston, who is not a designer, entered the children's fashion world, a bit of background story is needed: This Mary Institute and Country Day School graduate now resides in New York City with her husband, Eric, and their two children, Hannah and Alex. "My daughter was diagnosed with low muscle tone when she was about 19 months old," Johnston says. "She was in physical therapy for a several months…and a very important part of her life was keeping her physically active so she could catch up with her peers. One Christmas, I went to buy her a workout outfit—she wanted to mimic me when we were active together—and I couldn't find any high-quality activewear for girls her age."

In response to this conundrum, Johnston—with her finance background in tow—founded Kickety Split, the online girls' activewear company that launched on Jan. 1. While she doesn't design the clothing—she has a design partner who takes care of that—she deals with all day-to-day operations and strategy work. Despite the extreme undertaking of an online start-up company, she still teaches higher education economics and finance part-time.

From the Zippy Hoodie to the Sassy Skegging—leggings with an attached, ruffled skirt—these U.S.-made and manufactured items are color-coordinated for mixing and matching, all while offering play-ready quality and comfort. Details like inside-out French terry fabric offer fashion-forward choices, while contrast stitching brings more kid-appropriate color.

But there's more to Kickety Split than the clothes. Every purchase comes complete with a sticker set designed to be used as rewards for fitness-focused behavior, such as opting for the stairs instead of an elevator. "It's not just about the clothes—it's about enabling them to be physical active and healthy, and getting them started on these lifestyles at an early age."

To further that health-focused mission, the Kickety Split website features activity ideas, including such as the Down Doggie Pose, Ball Toss Circuit and Make Like a Tree Pose. "Whether it be physically active on the playground or getting parents a healthy recipe idea to make with their kids on a Sunday afternoon, it's [about] enabling parents to incorporate healthy habits into their children's lives early on."

This multifaceted online business features one more aspect: charitable giving. Johnston says for every product sold, $1 is donated to the Tom Coughlin Jay Fund Foundation, which supports the families of young cancer patients. "The charity component is a part of the business that's here to stay."

Currently, the company is focused on creating a summer line for girls, in addition to a new boy's line, which Johnston is scheduled to launch for the 2014 holiday season.

More Fashion & Living articles.