The only baby sweaters I've made were Elizabeth Zimmerman patterns. The Baby Surprise Jacket is fun, especially in self striping yarn, the only seaming is from the neck to the sleeve hems, along the top of the arm. This is the one I made for my son
The sleeves are kinda 3/4 length. There's a link on the rav page to a wiki for this pattern that talks about how to size it up, add length to the sleeves, etc.
I've also made a couple February Baby Sweaters, the body is back and forth on a circ, and then you pick up held stitches and knit the arms in the round. I made this for a baby shower a couple years ago.