Thumb guards are useful for preventing a baby from sucking her thumb while she sleeps to help break the habit of thumb sucking. Use a soft and flexible but firm material such as craft foam to create the two panels of the guard and a certain kind of sturdy thread to connect the two panels together.
Place the palm of your hand on a sheet of craft foam with your thumb extended and trace around your thumb with a marker, about 1/2 inch away from your thumb all the way around. Lift up your thumb and continue the line in an arch that extends down to where your wrist would be, around to the middle of your palm.
Cut out the the line you traced on the foam to reveal one side of the thumb guard. Place the shape on another sheet of craft foam in the same color and trace around it with the marker. Cut out the other side of the thumb guard.
Place the two pieces on top of each other with the edges aligned. Thread the embroidery needle and tie a knot in the tail end of the thread, about 1/2 inch from the end.
Pull the needle up through the two pieces, between 1/8 inch and 1/4 inch from the edge. Bring the needle up until the knot on the other end of the thread stops against the foam. Pierce the needle back down through the two sides, 1/8 inch from the edge and pull it all the way through to complete the first stitch. Continue around the edges of the two panels and don't sew the bottom edges together.
Tie a knot in the thread after the last stitch and slide the knot against the foam to tighten it and secure the line of stitches. Trim the excess thread from both ends with scissors to complete your thumb guard.