I suspect foul play...

So just this morning I finally got around to finishing my son's body tracing. I had traced him a couple days ago on a roll of brown packing paper and this morning he painted it. It was so nice out that I put it out on his picnic table to dry and weighted it down with a book. It's not very windy at all, so I left it and it's been fine. I've seen it out the window several times. Well, I put my son down for his nap and was in my bedroom for about an hour when I decided to go check if the painting was dry. I went out... and the painting is GONE! I searched all around the yard and path behind our house. The only thing I could think of is that it blew to the path and someone picked it up trying to be a good citizen. I'm so bummed!! It was too cute. I'm gonna have to redo the project with him sometime soon.