All you have to do is use gelatin and make a jello mold. I used 2 gelatin packets and added 1/2 cup of ice cold water and stirred. I then added 1 1/2 cups hot water, and again stirred. I poured this mixture into a pie pan and added magnetic letters (you can use any easily washable toys). I then put it in the refrigerator for several hours.
I popped out the jello mold, gave Caroline a spoon and let her have at it! She was unsure at first, but then dove right in. The gelatin doesn't have much flavor, so she wasn't inclined to eat it. She did thoroughly enjoy throwing the jello, however!
She got a couple of the letters out, made a HUGE mess, and then decided she was all done. She motioned the sign with her hands and informed me of this! Such a big girl!
We are definitely planning to do this activity again! As Caroline gets older she is going to love figuring out ways to get the letters (or other items out) of the jello.