For this Tiny Hat Barrette project you will need a small amount of two colors.
YARN: 4 ply US (10 ply AU)

HOOKS: 4 mm / US size 6

3.5 mm hook, US size E
a tapestry needle for sewing
bit of fiber fill for stuffing the hat
Some kind of marker to mark your rounds.
A small clip barrette, either of the kind in the picture below works nicely.