The ammunition of choice was mini-marshmallows.
But wouldn't you know it, we don't have any pictures of the fun the grandkids had when they were playing with the shooters. Luckily, when I was reading my niece's blog (Audra) she had made these, too, and got some pictures, so hopefully if she doesn't mind, I'll post a picture of hers instead:
The grands played with them again when they were at our house a couple of weeks ago. After they were all done, there were bunches of marshmallows everywhere. But they're gone now, so either the birds got them or some nice marshmallow fairy picked them all up.