It's pretty much just a conductivity detector (aka. water level detector) with the open leads stuck in a potty, and a relay on the other end that activates a favorite toy, in this example, a toy railroad crossing. Oh, and my 3 year old son built it! (With a little help... :-)
Details
Parenthesized names are Snap Circuit component IDs. (I don't know why this is sideways. It's not sideways in my photo viewer.)
There you go! To be more clear about the nature of our collaboration, I did the basic design, but my son put it together. Then, as it turns out, it didn't work because he had snapped the long bus that goes over the npn was TOUCHING the npn! My son came up with the fix, which involved taping over the errant short. (This is the orange tape visible in one of the pix.)
Thanks for entering The Hackaday Prize Uh Clem! I know some adults who could use one of these! Maybe add twitter interface for a congratulatory tweet :)
I know the snap circuits are rather self documenting - but ask the designer to upload a schematic when he has a chance - I'd like to see some more of his work! :)