It is hard to come by party hats with the age on it. Most of them are sold online and they can get expensive. This is a quick alternative.
You can buy generic simple store-bought party hats, like I did at Target (6 count). Then freehand draw or trace the age your child is turning. I have alpha punch out scrapbook paper which made this project even quicker.
Glue the age on to the party hat. Essentially, the rest of the 5 hats can be saved for future birthdays!