Give your kids a spot of their own, let them plan the garden, and choose what they grow in it. There are so many fun things to plant. As they get older, let them choose.
Teach them they can be creative with their garden spot. Show them all the options available for their garden. Go through seed catalogs or visit a garden center together. Let them choose the plants, the items, stones, colors, etc. Allow them to choose the shape and maybe even the location of their garden.
Even the smallest of kids can be involved in planning a garden. My kids like to put plants in the garden that are fun to eat, like ghost pumpkins, red, yellow, or purple carrots, blue potatoes, or purple green beans. They like to make homemade stepping stones and add other rocks from our property.
My girls love flowers and getting creative with colors. Occasionally, they have even been known to add old shoes or boots to their garden.
Being allowed to plan the garden themselves makes it such a treat for them!