KINGSPORT — When Jennifer Walker, a registered dietician, was a mother with four children in Kingsport City Schools, she had issues with school meals.Now, with a year under her belt as supervisor of school nutrition and only two of her four children still in KCS, she has a different perspective.That is based, in part, on her new knowledge that student tastes drive menus but that those menus also must meet numerous federal requirements.Among the most popular items?