This is a headband I have knitted in one afternoon to match a pullover that’s not quite finished yet.

The finished width in this case is 12 cm / 4.7 in so it might not be suitable for small children unless you use a thinner yarn and smaller needle size.
As you only need about 100 m / 110 yards, this is also quite a nice way to get rid of scrap yarns and leftovers :)

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Errata:
I wasn’t quite clear in Part 2 of the pattern by omitting to mention that you slip the first marker and knit the pattern to the second. The 4 pattern rows should be like this:

Row 01: k2, p1, k4, p1, sm, (k1, p1) to 1 st before m, k1, sm, p1, k4, p1, k2
Row 02: k1, p1, k1, p4, k1, sm, (k1, p1) to 1 st before m, k1, sm, k1, p4, k1, p1, k1
Row 03: k2, p1, C4F, p1, sm, (k1, p1) to 1 st before m, k1, sm, p1, C4B, p1, k2
Row 04: same as row 02