Wow, such a wonderful idea! How about those daisies, sunflowers, marigolds, lilies? There are a number of shrubs and herbs that barely grow more than a foot; are easy to maintain and look good too. Also, there are a number of plants that are just a height of the grass and bear lovely flowers.

Good luck and please do keep us updated.

What about growing Yarrow, Purple cone flowers, or Aster for attracting butterflies? Most shrubs I think will grow taller than you want. But you can always cut it back. Like w/ the Butterfly bush, you're in a warmer climate than I am, and mine dies to the ground in winter and comes back from the roots. So couldnt you cut it down to the ground in early spring, then just keep trimming it while its growing? It'll get really bushy then. Or you could try something like bush beans for bushes, and she can eat the beans. They have purple and yellow ones, could make veggies fun for her!

Salvias all attract butterflies. And since they are related to the kitchen herb sage they are non-poisonous. Some are annual/perrenial depending on your climate. (Lots of perrenials in z9!)
They can be trimmed as a short hedge, but the are deciduous, so it'll be a bit bare in the winter.
There are lots of types--if you want more info, goto GW's Salvia forum. (I've never posted over there, but sometiems they have pics, so I lurk.)

Hibiscus and Turk's Cap (a native hibiscus whose flowers don't unfurl but does well in part shade) can be trimmed as a short hedge--but you have to be vigilant about trimming! I know the flowers are edible, but I don't know about the foliage.

Ruellia (Mexican petunia) grows about 3' tall (as long as you don't buy the "Katie" dwarf variety.) It has a similar look as bamboo, with petunia-like flowers on it. It comes in purple, pink, and white. You'll have to check on it's toxicity, but it's great for kids because the flowers only last one day so they can pick them to their heart's content!
Caterpillars like to eat it, so it's a butterfly host plant.

Larval host plants that also have flowers for the adult butterflies are great for kids because they can see the complete life-cycle (and what kid doesn't like to watch caterpillars?)

Vicky's blog!

How about some easy to grow vegetables? That way you can tie gardening in with other activities, like helping in the kitchen. Some bright flowers might also be nice.

Nasturtiums and calendula are non-toxic and edible, plus they are pretty colors, easy to grow and kids love them!

My daughter planted four o clocks that reseeded themselves, Now any that come up are her flowers and she didn't have to do a thing this year. She was also facinated by the fact that they don't open till it's darker.

Oh and pansies and violas are edible so if you put those in it won't matter is she tries one.