Another cool thing you can do is to make bows or other hair accessories (because Hello Kitty loves her hair accessories X3) of several colors and attach them to safety pins instead of sewing them directly to the brain protector. Interchangable hairbows= New brain protector everyday!
Eyes and nose: Crochet regular circles or use buttons or patches Bow: Crochet 2 circles (3 rows in the round) and attach them with a smaller circle (1 row in the round) They sell hello kitty safety eyes and noses but those can be irritating for a brain protector unless you decide to put a lining in it.
You don't really need a specific pile of flesh for a hello kitty brain protector. Just make a basic brain protector in white, then make 2 cat ears and attach them to the top, then make the bow, eyes, and nose. Easy =)