Three-year-old Clara Centola seems unconcerned by the adults around her as she works at a mini-kitchen, deciding which cloth-toy fruits and vegetables to serve her imaginary guests. There are no plastic fast-food replicas to choose from at her Oklahoma City preschool, where the real food is vegan and gluten-free…

At the Sunflower Preschool in Boulder, Colorado, children learn about composting and recycling, and planting and harvesting gardens. A rotting log, for example, isn’t just a deteriorating piece of bark, but a way for children to investigate where bugs live.

“We feel that anything you can learn inside, we can learn outside,” said Sunflower Mars, the school’s co-director. “We let them be self-guided.”