I tried to post this in a comment but it didn't work.
I made this surprise jacket following the Baby pattern in the Opinionated Knitter, using Elsbeth Lavold cotton patine on size US 5s. the only modification I made was to cast on the increased number of stitches after the cuff shaping. I wanted to pick up and knit sleeves down from this point, but i haven't done that yet.
here it is on my son, 6 months old at the time:
it's little long for him, but fits well. the sleeve length is great for a crawling baby, the width since i left out shaping is a bit extreme.
here's the same sweater on my 4.5 year old:
the sleeves fit her well as short sleeves, and the sweater fits her as a close-fitting sweater that hits right at her natural waist. perfect for ballet class.