Although school might be out for most people right now, you can still use the summer garden to help teach your kids about the plant life cycle. Try growing beans in a cup, or plant some partially grown plants — like tomato plants — in your garden to show your kids the circle of life, er plant life. Check out THIS ARTICLE on how homeschoolers, non-schoolers, parents or teachers can teach kids about plants.
Consider starting your own herb garden, just buying a few potted plants to encourage the little scientist to get interested in plants. Use the summer months to let them journal about how the growing plants change. Check out the book "Get Growing" by Louis Walker for into integrating even more plant projects!