Some of my happiest memories are playing under my grandmothers big (huge actually) arching shrub that in San Antonio we call 'primrose jasmine'. (Edited thanks to Lorelei) It's very fast growing, takes alkaline soils, deer proof, grows in sun or shade and seldom needs extra water, especially in partly shady locations, and here it's evergreen.

Primrose jasmine

For big leaves how about elephant ears? The upright varieties don't take as much water as others, some of which in their natural habitate grow in standing water, but all varieties still need some water. Perhaps planted along a shed where they could get rain off the roof would be good.

Another big leafed plant that's fairly drought tolerant where they could play between the tall stalks is 'root beer plant'. Not sure about the deer on that one. The leaves are big and soft and smell like 'root beer'.

'Root beer plant' Piper auritum

For soft maybe collect leaves to go under the primrose jasmine, root beer plant and elephant ears providing a soft bed of leaves and keep them off the pure dirt and rocks. Lamb's ears are soft to the touch, but easily bruised by little feet and hands.

For flowers they could pick Mexican hats all summer around here. There are many others as well. You'll be getting lots of ideas from folks on this forum.

Roselee, is the jasmine your talking about also called Primrose jasmine? That's what I call mine but it's a different variety than what you mention:

http://www.floridata.com/ref/J/jasm_mes.cfm

I agree with the root beer plant but mine likes dappled sun. How about any of the native honeysuckles on arbors. That way the kids can pick the flowers and suck the nectar out of them. Culinary sage has soft leaves. Split leaf philodendron has big leaves but prefers being protected some from the sun. In most areas it's deer resistant. Another big leaf plant is the one commonly called Bear Britches, a type of acanthus but again, it likes shade. I got mine at Shades of Green.

What a fun opportunity. How great for your kids to express their interest.

Several canna lilies placed a few feet apart can provide a dense grove for hiding in a single season and are commonly available in heights to 6 ft. They're surprisingly tough; in Dallas, they've grown and flowered for us in dappled shade through full sun on a south facing brick wall.

Our kids got a kick out of planting mammoth sunflowers when they were young. Something about a plant that can grow well over 8 ft from seed in a single season and has those giant flower heads.

build a wooden teepee structure and plant passion vine around it. that blooms almost all year here and the butterflies love it

Lorelei, you are right. I couldn't think of the correct name of primrose jasmine at that moment.

I'm not sure about deer resistant but elephant ear plants came to mind when you mentioned that they want to hide behind the plants. Horsetail reed also grows up straight and tall.

Lamb's ear plant has a fuzzy, interesting feeling to the leaves.

Trumpet lilies also can get very tall but I don't know if it takes a few seasons for that.

This year, I'm also growing a butterfly bush, which averages up to 6-feet tall and wide, so that will be a huge plant in my garden also.