Obesity is a real and present problem for children. I would say that a healthy lifestyle is as important if not more important than conventional subjects such as math and literacy because no matter what career you choose you still need to maintain a healthy lifestyle. You can get by in many careers just fine with only a basic understanding of math.
Because,if not done while a kid it is very difficult to maintain a healthy weight when you've gotten older .It can cause heart problems and in rare cases cancer. After a child has gotten used to the habit of not staying fit then when gotten older they will no longer want to and this can lead to death not occupying their time with physical activities