Wild Ginger (www.wildginger.com) has a free pattern drafting program with some patterns sized for preemies – I don’t remember if it goes to larger sizes.

Martha Pullen has some heirloom sewing patterns (smocking, lace insertion, and embroidery) that are based on techniques used on clothes made for babies & children in the past – they are usually used for dressier events (christenings, photo shoots at various holidays, or because Grandma loves the techniques) in modern times.

Another option is to buy a baby garment at a thrift store or garage sale and carefully take it apart to make a pattern from it. Take notes on how you take it apart, then start at the last thing you did and reverse things to put a new garment together after. If it works well – trace it on paper to keep as a "master pattern" for yourself with notes on the direction of stretch, location of snaps or buttons, how many you need to cut of that pattern piece (two sleeves, one front, one back, two fronts for pants, etc.).
References :

http://www.angelfire.com/planet/mcshelpsite/sewingstuff/freepatterns.html/
References :