I have a chicken coloring book, and the pages are just perfect for envelopes. Do you have any coloring pages, blank or colored, that could be turned into envelopes too?
Here is a good example of what framing can do. I'll probably make the address a speech bubble from this grumpy bird.
You could color these pages in either before or after they are folded up.
I'll color this in once I decide who it is going to. It's fun to match your envelope to the recipient!