Unfold a paper party hat to create a pattern. Draw pattern on back side of polka dot felt. Cut out. Repeat for as many hats as needed. (You can also use the paper hats as a base for the felt hats, just glue over paper one.)
Glue pom pom trim along bottom edge of hat. Overlap and glue back seam. Glue elastic to either side of hat.
Cut pom poms from remaining trim and glue to front of hats or add Iron on numbers for the age of the child's birthday.