I think you'll love the simple approach in these two books. It starts with a little bit of dirt and the simplest of tools and goes from there. I loved the appreciation of the value of flower gardening and rather than buying everything at the nursery, instructions are given for growing new plants from starts from other plants. It's a very natural and simple approach and is presented in a way that a child can see what he needs to do to grow a garden, which can be as simple as a garden in a little box.
 
Paperback 5.5x8.5 373 pp.