I really like chives because on a tour (or anytime) people can pick off a leaf and eat it, and kids don't know what it is. Beautiful Flowers, Too.
Mints are also good this way because the grow so fast and are good in pots. You could have a "mint garden" and people could sample different types of mint and see if they could tell a difference.
Edible Flowers are good - who has eaten a flower, but it's a bit of a thrill right? Naturtiums, miniature roses, violas, calundulas, borage.
Bee/Butterfly plants - anything that's going to be covered with bugs can be fascinating. Think blue flowers!
I also think live animals are a big draw for children and everyone... a tiny hen house/run and/or fenced bee hive is very interesting indeed.
Stuff people can eat and stuff people don't know how it grows til they see it is good. Think prolific and easy.
Brambles top the list in my mind. Alpine strawberries are fun and easy. You can start a bunch from seeds and get a bit of fruit the first year.
Snap dragons and other flowers that "do something" - I always was taught to squeeze the cheeks of the snapdragons to get them to open their mouths, and that was fun in the garden.
Kids love Edible
Pea Pods on a
trellis, too.
Bean pole teepee or something they can climb in/sit on. Weeping mulberry also comes to mind. They want to be IN THE BEDS exploring.
Am I going down the right track here... are any of these what you were thinking?
Emily