One of the most important thing that any runner can do to avoid injuries is to properly cool down after practice or a meet. The first step to an effective cool down is to keep the body temperature from dropping to quickly – to avoid this from happening athletes will put on sweats (pants & top) during the cool down. It gets very cold at sundown as well and sweats will help. Please make sure your athlete has sweats & water in their bag each practice.
Here is a video that will explain the cool down.
How to Cool Down After Running — powered by http://www.livestrong.com