Nothing beats container gardening to introduce children to environmental awareness, the fun of caring for something through its entire growth cycle, and the joy of digging in the dirt.
We love the oval shape of the Somerset Planters - they have a remarkably small footprint and planting a container garden together is a fun way to bring a little summer indoors. Prices range from $29.95-$69.95, depending on the size. In our experience, nothing beats gardening with children, and if you plant something fast growing, a container garden can transform itself into a pretty impressive small garden in just a few weeks.
Not sure what to plant? Earth Easy has a great list of child-friendly plants to grow.