Today’s kids can’t keep up with their parents. An analysis of studies on millions of children around the world finds they don’t run as fast or as far as their parents did when they were young. On average, it takes children 90 seconds longer to run a mile than kids did 30 years ago. Heart-related fitness has declined 5% per decade since 1975 for children ages 9 to 17. The American Heart Association, whose conference featured the research in 2010, said that this was the first report that children’s fitness had declined worldwide over the past three decades.⁠ ⁠ “It makes sense. We have kids that are less active than before,” said Stephen Daniels, a University of Colorado pediatrician and spokesman for the Heart Association. Health experts recommend that children aged six and older get 60 minutes of moderately vigorous activity each day. Only one-third of American kids do now.⁠ “Kids aren’t getting enough opportunities to build up that activity over the day,” Daniels said. “Many schools......