I came across this post recently and knew it was something I wanted to make for the kids. She has a great tutorial on how to make these, so I'll let you visit her blog for that.
Instead of the mouse picnic theme the original poster went with, I decided on an ocean theme for our rocks. The kids and I went out searching for rocks in the park near our home, and then took them out back to wash them. I filled a plastic tub with soap and water and let them scrub down the rocks. Then, while they were busy watching a movie I cut out simple ocean themed shapes from fabric and adhered them with ModgePodge.
I was pretty happy with how these turned out, but as my husband pointed out, a rock, no matter how cute, is still a rock, and there is always the chance that one of the kids might decide to throw it (not good). We decided to use them in the lentil trays, because knowing my kids like I do, they are only going to throw a toy if they are upset and fighting over it, and that never happens when they play with the rice and lentils because they play separately. Another option I might do is to use them as decoration in my son's room, which is fish themed. They'd be cute sitting up on a shelf, just as display items. At any rate, I thought these were fun to make, and I was certainly satisfied with the project. Thanks, Red Bird Crafts, for sharing!