Supplies: You will need felt (.25 cents at Joann), a small spool of yarn (1.29), a yarn needle (.99 cents for the plastic ones), and a Sharpie.
Simply make a template to cut out your "flags" from your felt. I used scissors to cut my felt, but a rotary cutter also works great and speeds things up quite a bit.
After cutting out your flags, simply string them together with your yarn and yarn needle. I am NO sewer (sorry Mom, still trying), but this was crazy easy. I didn't measure anything, and didn't always sew in a straight line, but Im from the thinking that eye-balling it makes it look more playful/natural. swear.
Last, get to work with that Sharpie marker, writing out a message if you wish. You could also leave these bare to just use as decorative garland.
Happy Bday Banner'ing!