Bang-Flag Gun

 For Goodnight Moon  there is a bit where one of the characters uses an old cartoon-y bang-flag gun. The guns themselves can be purchased fairly easily online. The mechanism they use is surprisingly easy.

 The barrel is actually two pieces, attached at the end with a spring hinge.

 the flag is rolled up and hidden inside the folded barrel.

 The flag is weighted at the bottom, so when the barrel is opened the flag falls out and unrolls.

The trigger mechanism is just a simple lever. it wedges in place to hold the barrel shut and a quick pull allows the spring hinge to release and the barrel to open.

The guns I ordered online worked fairly well (I ordered extras just in case they fail later, they're pretty cheap and I don't entirely trust them), but they looked a little silly. The handle was too tiny for such a long gun.
I purchased three guns from the dollar store to use to beef up the handles.

After some experimentation I ended up using just one small piece of the dollar-store gun handle as an extension on the existing handle.

I secured it in place and smoothed out the seams using epoxy putty.

Finally I added the guard surrounding the trigger to give the gun a finished look.

You can see in the previous picture that I attached the trigger guard to both the barrel and the handle. I quickly realized that attaching to the barrel prevented the spring mechanism from working. I removed the epoxy putty from that connection and let the connection at the handle support the whole piece.

When the guns were assembled I covered the parts I wanted to remain silver with masking tape, and sprayed the handles brown.

I think they turned out pretty well, and much less awkward in scale than they were to start.