On a beautiful summer day, a group of rising third-graders gathered in the Columbia Heights Public Schools’ fruit and vegetable garden. Their mission: identify bees pollinating the flowers. One group of children followed Melissa Trent, the district’s agriculture specialist, to a sunflower. “You can touch the flower,” Trent told them. “Gentle hands.” A child gingerly brought a finger to the center of the flower, and grinned. “Does it feel like i…