I would suggest any of the classic runner beans like Painted Lady, Scarlet Runner, Scarlet Emperor etc. They have plenty of big leaves and beautiful flowers.
And if you leave the bean pods to dry they'll make enormous beautiful spotted beans that the kids can use for playing Jack-in-the-Beanstalk. You know what might work to fill in the gaps with pretty flowers might be one or two morning glory vines in between the bean vines.

Here's a good article I read recently - she's in the Santa Cruz mtns of central-north California, zone 9B or so.
http://www.growbetterveggies.com/growbetterveggies/2008/08/how-about-a-veg.html

Oh, but it just occurred to me that Morning Glories are poisonous. So if your little ones are prone to munching in the garden like mine are, then you'd better stick with just beans!

Plant Nasturtiums instead if morning glories. All parts of nasturtium are edible, and taste peppery.

Although you say you don't care about the fruit, be aware that if you don't pick your runner beans as green beans they will start to ripen and will stop flowering, considering that their reproductive job has been done. You will also be missing out on a delicious vegetable crop.

Runner beans also need rich, cool, moist soil so you will need to water assiduously if they are growing in pots. Maybe the kids will do that for you.

leggs, something makes me think you may have meant "pole beans" rather than "runner beans", although either would suit your purpose.

I like the idea of filling in with a second type of vine, perhaps a shorter one because the spaces between poles will be wider near the ground. Nasturtiums sound like a good bet for that. Be aware that some nasturtiums have more of a vining, climbing habit than others, so get the right kind. Cowpeas are another possibility for that.

Jim

Scarlet Emperor and painted Lady are the good choices for your needs.They produce very beautiful flowers accenting to your garden as well as produce beans that you can use as a veggie. These beans have perennial roots. Now instead of fixing poles in each pot it would better to fix a pole in the center and place the pots surrounding the central pole.Tie the threads to the pole at one end and fix the second end of the thread in each pot.Guide the vines on these threads to the central pole as they grow.

I am posting a pic. of a runner bean from my garden.

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If 'threads' are used they need to be stout string and very firmly tied to the pots. The pots would also need to be very firmly anchored to the ground. The weight of a runner bean plant in full leaf, especially after rain or in wind would pull the pots over. We are talking about a plant that will grow 10 feet tall. And although perennial in their native habitat they will not overwinter if the ground is likely to freeze or be damp and cold through the winter.

Chaman - does your photo show a non climbing runner bean? It is unusual for them to flower so low down before they have grown a few feet tall and I don't see any tendency to twine around those stakes.

Flora - These are 7 to 8 feet vines twining around the Dwarf Moringa oleifera plant.This pic. was taken to illustrate the kind of flowers running beans will bear.I am posting two more pics. that shows ( barely ) it's twining nature.