So, you want to make super-fantastic sock puppets that all the neighbor kids will be jealous of? Well, I guess I can let you in on my little secret. It is a piece of plastic in the mouth.
Here's how it works: Get an old milk jug and cut out a section of flat surface.
Now, fold that piece in half and cut a couple of ovals out. The size of your flat space will determine how many ovals you get out of it. And, your ovals should be about the size of your little one's finger-to-thumb space where they would normally stick the sock puppet mouth.
I can usually get two ovals out of a large flat. One..
and two. These don't need to be perfect, they are just going to be inside the mouth to give it some permanence.
Now, this step is really important if you want to spare your fingers glue gun misery. Push the toe of the sock inside to make a pocket. Don't go too far back, just a couple of inches. Test the space by sticking your plastic oval in it. The folded edge goes in first and should hit the toe of your sock, the rounded edges should about sit on your socks lips.
Now that you have your sock in position, take your cut and folded plastic between finger and thumb,
and run hot glue along the edges of both sides. Don't worry about that spot where you are holding, you can go back and get that later.
Now, this is the trickiest part of all. Really, it is persnickety. And I am not just saying that 'cause I like the word. You need to slip that hot-glued plastic into the pocket you created for the mouth, but you don't want the hot glue to touch the sock until it is in place. Just slide it in and squish it down. But, don't squish too hard or you will glue his mouth together. (If you need to do this for therapy since you can't do it to your kids, go ahead, glue those lips together.)
When you have this done, you can go back and glue those little spots on front and back where your fingers where.
Once you get the mouth in, it is the traditional stuff - eyes, hair, etc. Okay, I only do eyes and hair. But let me tell you, this little plastic bit makes the sock puppet SO much more functional! It will get played with far more often, because the mouth works! Hope you have fun!