A herd of toddlers runs across the springy gymnastics mat, each to a small square of carpet. Their parents follow close behind. Once seated, coach Marci Schuster takes them through some warm-up ...

Lucy Brown somersaults backward down a ramp, leaps over a mat, rolls across a platform, jumps a series of hoops, squats into a yoga pose and hops over a row of cones. And all with her diaper intact.

For kids who might be struggling with potty training, a classroom is giving them the skills they need to move on up to the big potty league.Melissa Adam hosted her first "potty party" six years ago, ...