Ages 4-5: For kids in this age group, gardens make great playgrounds. Encourage secret hide-a-ways, such as forts made from giant sunflowers, or a teepee enclosed with climbing pole beans.
Let them pick some flowers and dismember them – try bleeding hearts, snapdragons and daises. Give them their own kid-sized tools and a spot to dig and water. Show how plants start from sprouted seeds. Help them sow some large seeds in pots – radishes and marigolds, for example – so they can experience the birth of a plant close up.