Gardening is definitely a creative act ... and one that is wonderful to develop with the kids. In His Image listed quite a few gardening books that I like, but I did want to add this one: Gardening with Kids by Catherine Woram and Martyn Cox. This is definitely a keeper -- and Amazon currently has it for 58% (!) off the regular price. The authors of this one understand kids and what they want to do when they garden.
Packed with tips and explanations and clear photographs, this book includes planting ideas, crafting ideas, and game ideas. There are lists of plants that kids should plant and ones that they shouldn't (either because they're poisonous, difficult to grow or hard to work with). The craft ideas include crafts to make using natural things from the garden (including a really cute elf set made with twigs), crafts to make to attract nature to the garden, and gifts to make from the garden's bounty such as pretty seed packets and lavender sachets.
This book is definitely a must if you want to nurture creativity with your kids in the garden!