Plants are endlessly fascinating, and the first time your child realizes that a tiny seed is actually a cunningly disguised manufacturing plant for flowers and vegetables, your landscape, windowsills and patio will become a playground for experimentation.
Start indoors with peat pots, and choose plants that have large seeds that sprout fast, like pumpkins, sunflowers and sugar peas. Mark the seed start date on the calendar, and encourage your child to keep a plant diary and take lots of photos. Children find fragrant seeds or seedlings very entertaining, too, so try herbs like lemon balm and mint alongside faster growing plant varieties.
When temps warm up in the spring, move the project outdoors by clearing and prepping a portion of a flowerbed for your child's garden. Provide him with some child-sized gardening tools, include some vegetables, and be creative with your choices. Even if your child hates veggies, he's bound to want to try some he's grown himself, so take advantage of the opportunity to introduce your budding gardener to some new and interesting greens.