First, core your apple. The original blog post on Babble kept the apple's core to make the finished snack look more authentic. I would rather sacrifice a little realism for an easier to eat apple, especially for a child as young as mine. Who am I kidding? I'd core the apple if making this snack for myself, too. See the bad spot on the right side? That's where I cut the hole for the worm. Don't be afraid to use a slightly blemished apple.
Cut the cored apple in half.
Cut a large marshmallow in half across the long side. Stuff one half into each cored apple (to keep the peanut butter from coming out the top and bottom).
Use a stiff, heavy duty straw to cut a small hole in the apple. I used the plastic straw from one of Grace's sippy cups.
Poke the worm through the hole. I struggled with this gummi worm for a good three or four minutes before realizing that it had a head and a tail. I have never before seen a gummi worm with a head and a tail, but I suppose I'm not all that up on candy culture these days. It goes into the hole much more easily if you put the tail end in first.
Use a scoop or a spoon to fill up the remaining holes with peanut butter.
Stick the two halves of the apple together and serve!