Also, it's easy to lose your sense of direction in the park. I've seen people wonder why the girls didn't run for Abby's house, but it's very easy to get turned around in there. And unless they've actually walked from there to the park before, they may not have even been sure how to do it. We're looking down at the distances from a map. It's easy for us to see the way. They weren't. They most likely only ever drove to the park in a vehicle. There are lots of fences, embankments, etc. along the way, too. It wouldn't have been smooth running.
My guess is that, in a panic, they just ran.