Another cute idea from my teacher friends.
What you don't see is, inside the "door" of the D is a picture of the child with his pet dog (this could be a homework assignment that the parents can either print out and send to you, or email to your school email addy). For those children without a dog, they can either cut out a picture of a dog from a catalog or magazine. Or you can snap a photo of them with a stuffed dog toy. (Email the pic to your school email addy, then print out.)