How many is a few weeks? I'm guessing not enough if you want to see actual flowers. A lot of annuals you can get to flower in approx. 12 weeks. That seems to be fairly average for the fastest of flowers.

Beans are pretty quick and satisfying for kids. Good for you for doing this =) I still fondly remember our grade school bean experiment (has something to do with my current plant obsession.) We just stuck bush bean or pole bean seeds into clear plastic cups we cut drainage holes into and filled with wet paper towels. The teacher made sure that we kept them moist and sunny and 5 days or so later they were sprouting and I was forever hooked on watching plants grow.

Yep. I am afraid you are going to have to teach them patience as well. I did have Alyssum start little flowers in a bit less than 4 weeks, and Thumblina Zinnia is settting buds a month after sowing, but that is with a decent light set up, not on a window sill.

Some lettuce can be ready to eat as baby greens in four weeks (again with lights), so you can get them excited about eating vegetables too!