Why shouldn't adults run in kids' shoes?
Kids' shoes are specifically designed for feet whose shape is different from that of adults.So, a kids' size 5.5 does not necessarily have the same volume as required for an adult size 5.5.Kids have longer, narrower feet, and the shoe shape is specially designed to take account of this characteristic in children, whose feet are growing.Also, there's not enough cushioning for an adult when the shoes are used for running.