2.5 mm needles, 36 sts, basic twisted, broken rib sock pattern. Would fit the average six-month old niece.
Those socks were so cute, that I immediately cast on socks for her big sister:
2.5 mm needles, 48 sts, basic twisted, broken rib sock pattern. Shooting for a kid's size nine.
And for a comparison, here is one of each together:
Oh my! These are too cute! Because I am dorky, I weighed the socks. The wee socks are 15 g, and the big sister socks are 28 g. I'm using Wisdom Yarns, Marathon - Los Angeles (gah! This has been in the stash for a while - too lazy to find a good link).
I've cast on, in the same yarn, a pair with 44 sts. Those will be for the cousin.
After that, looms the big question. What do I do for the boy? Purple and lime green are too girly, otherwise this yarn would be perfect.