on top of these two pieces to see at what level on the main mitten piece your thumb piece needs to sit. this (below) is just right for my daughter. trim your thumb piece (pattern piece b in photo below) to the width and height of your main mitten piece.
looking good. and now we need to make another piece to connect the bottom portion of the inside of our mitten to the top. and this is where it gets a little, tiny bit hairy. not too bad, but a little.
so now you have three pattern pieces for your mitten- an outer main piece, an inner lower piece, and an inner 