The University of Missouri Extension runs a program called the Kindergarten Farm Food Initiative. A newsletter to parents from the beginning of the school year states (emphasis in the original):

your child will enjoy locally grown fruit and vegetable snacks three times a week.

It also characterizes locally grown food as “fresh” and “delicious,” and admonishes parents:

If your child asks you for a tasty fruit or vegetable snack at home, we hope that you will encourage this healthy habit.

Serving healthy snacks to a class doesn’t endorse any particular ideology. And, by itself, a visit to a farm isn’t indoctrination. (I applauded when this school took kindergartners to a farm to learn about agriculture.) Where this program crosses the line is in its newsletters, which are based on the assumption that locally grown food is inherently good. I would guess the same attitude toward local food is conveyed to students during class time.

To explain my objection with an analogy, suppose a school, in connection with a unit on China, announced to parents that students would play with fun, high-quality toys from China three times a week. Suppose it sent home newsletters about the toys emphasizing the fact that they are from China. Wouldn’t that be seen as an unfair endorsement? Everyone agrees that kids need to play, but whether toys from China are the best choice is debatable. Even if the school didn’t explicitly tell the kids that toys made in China are better than other toys, a kindergartner could easily form that conclusion if the school made no mention of toys from other places.

It’s fine for a school to tell kids where food comes from, but it shouldn’t focus on one food source to the exclusion of others. Parents can always tell their children that local food is preferable, if that is something that their family values.