I teach Sunday school to 3-4 year olds and this year as their graduation gift I am growing sensitive plants for each of them. I found the cutest seed and mini greenhouse kit online at the Tickle Me Plant Company. (www.shop.ticklemeplant.com). In case you don't know, this is a type of mimosa that reacts to touch and droops, then comes back up after a few minutes. It's the single best way I have found to get young children to fall in love with plants! 

Here's a link to a video showing the plant in action! www.youtube.com/watch?v=BVU1YuDjwd8 ...