If you’ve ever wielded a stroller carrying a baby while running, you know just how awkward and difficult it can be. You can’t swing both of your arms freely at once, your stride is sometimes cut short, and no matter how “lightweight” the stroller’s packaging promised it would be, it’s a beast to push up hills. Now imagine that you have to push not one, but five kids in one—and for 26.2 miles. That will give you an idea of what 37-year-old Chad Kempel experienced at the Surf City Marathon in Huntington Beach, California, on February 3. Kempel is a...