A lot of these Essentials of Education seem like no brainers, and this one definitely is in that family. However, we have to teach kids overtly to take care of themselves. Unfortunately, a lot of the aspects of our modern lifestyle lend themselves to an unhealthy life. Ironically, technological improvements may have made some parts of our lives more convenient, but not more healthy. We have instant fast food (but packaged food does not give us fresh food or the essential nutrients), instant access to information (so we don't have to get off our duffs to find out things, and instant action, (video games instead of exercise).
I'm not going to get into a debate here about the role of the family here. It is just a fact of today that schools must teach children to make healthy choices and to teach them to take care of themselves. This includes eating right, making safe and positive choices, exercising, knowing how to relax, managing stress, etc.