How to do it
Download the templates. The adult hat measures 22 inches around (fits a medium size); the child's hat measures 21 inches (fits ages 6 to 10).
Wash, dry, and iron fabrics.
Print and cut out templates for hat brim, side panel, and crown. Lay templates on first piece of fabric, trace with marker, and cut out. For a stiffer brim, lay brim template on fusible interfacing, cut out, and attach interfacing to wrong side of brim fabric.
With right sides facing, machine-stitch center-back seam of side panel with 1/2-inch allowance. Press seam with iron. Repeat with brim.
With right sides facing, pin crown to side panel. stitch with 1/2-inch seam. Trim seam allowance to 1/4 inch, and notch to ease curve.
Repeat steps 2 through 4 using second piece of fabric.
Returning to first fabric, pin brim to side panel, right sides facing, aligning center-back seams, and stitch with 1/2-inch allowance. Notch seam to ease curve.
Repeat step 6 with second fabric, but leave a 4-inch opening.