Knit this snug as a bug sleep sack with the free pattern by Robyn of A Devine Life.
Robyn writes:

All babies need a bit of extra snuggle when first born, and sources tell me they should also be wrapped up tight. But what if your babe likes to kick her legs?
I fell in love with the Kicking Sleep Sack some time ago, but with such small needles, my hands revolted before I could finish up a bag. Here then is my worsted-weight counterpart. By using slightly thicker yarn, this pattern will practically knit itself, while still keeping everything soft enough for even the most sensitive of babes! And as an added bonus, you use the entire skein of yarn, so there’s no need to figure out what to do with leftovers!