Nike Infant Flex Runner 3 An easy-to-pull-on design and grippy outsole make the Flex Runner a fan favorite. Made with playgrounds and spontaneous games of chase in mind, this iteration has the stretchy bootie kids love with synthetic leather overlays for durability. A flexible outsole helps provide multi-surface traction, so little ones are always ready to play. Style code: FN1478-400 Nike Infant Flex Runner 3