I used felt for the hats, the kind you can buy by the yard. It was made for adult-sized heads. It would need to be scaled down for a small child.
Cut the shape in the second photo, with the short, straight edge on the right on the fold.
Stitch, right sides together, along the top edge, shown in the third pic.
Flatten the back point with the seam centered, as shown.
Stitch a curved line through all layers. I made a cardboard template to stitch next to so that all the hats would be the same.
Cut the excess corner away above the stitching line. Turn the hat right side out.
Fold up the brim on the back of the hat 2 inches. Press with steam iron.
Fold the remaining brim up, tapering toward the front and ending about 1/2 inch on each side of the seam at the front.
Hot glue the feather in place.