It's really simple, I have 2 healthy non-obese kids, we do not allow sugar/crap snacks/drinks/meals. Computer time is limited. They are mostly drinking water when thirsty. The adults in the house set an example, the Wife and I run and attend a gym. The kids see us come home and ask what we did, and they want to exercise too, I have them do sit ups and pushups and jumping jacks and other simple stuff. My 7 year old daughter attends an early school program for running, 1 hour each week before school. In the spring I will run a school 5k with her. This is the goal of the year long program. In the warm months kids play outside and are in sports.
We do not shop at Trader Joe's or Whole foods, we shop Meijer, Kroger, Big Bird, and Costco. We have cut way back on red meat, and eat chicken and turkey. Don't get me wrong, we still have deserts/chips/cookies for the kids as a "Special" for rewards. We order pizza occasionally as a family treat cheat meal. We are not nazis. But being active and putting in the TIME is what is needed. SO many parents just give them pop and junk to pacify the kids to get them out of their hair.