Tired of leaving your little ones at home when you head out to the gym? Kori Sassower and Robin Hoberman have a solution. In April, they opened Momentum (4 Manhattanville Rd, Purchase 201-693-2770/516-692-3627; momentumclassroom.com), a boutique fitness studio designed for kids between the ages of 10 and 16 that offers boot camps, sports training, and classes in cycling, Zumba, cardio kickboxing, and core fusion. “Exercise is a part of who you are, not something you have to do,” says Sassower. “We teach the kids proper techniques and enforce a positive attitude while promoting physical fitness.” Momentum also offers private and custom classes and birthday and camp parties. Another program, Momentum Jr., is designed for youngsters between the ages of 3 and 9; classes are held off-site as after-school programs at schools or special events at local day camps.