It's a simple garter stitch band knit on straight needles and fits most heads! It fit my 4 year old's head and my adult head! It just ties in the back making it very simple with no seaming. Here's the pattern (also found in downloadable pdf format on my sidebar):
Worsted, medium, or double knit yarn, in two colors
With first color, CO 40 sts.
Rows 1-3: Knit every row
Row 4: Join second color and knit entire row
Row 5: Knit
Rows 6 & 7: At beg of row, CO 40 sts., then CO those 40 sts. and knit rest of row.
Rows 8 & 9: Knit entire row
Row 10: Join first color and knit entire row
Rows 11 & 12: Knit
Weave in ends
PS...There's a cool new website with some FREE adorable kid's patterns. Go check out Petite Purls!