Here is a very, very simple pattern for a child's chevron cowl.
Just one pattern row repeated throughout as many times as you wish to make the width you wish.
As for the starting chain, chain any multiple of 12 + 2 to get the length you wish.
Using 1 skein worsted weight yarn (or oddments of Green, Red, and White), and a 4mm hook, this works up very quickly, and you know I like simple and quick!
12 sts and 8 rows dc on 4mm hook = 4"
100 yards of Worsted weight