The pattern calls for aran yarn, but I got gauge on the first try in the worsted weight Liberty Wool on size 8 needles. I knit the 24-month size, the largest of the "baby" sizes, and although Lil One turns two in a few weeks, I believe this will fit her all through this coming winter and spring.
I think I like the matte buttons with shanks better than the shiny buttons with holes, but my local giant-craft-store didn't have enough of them, so I just used them for the center(ish) owls on the front and back. Finished sewing on the buttons on Wednesday, August 8, comfortably ahead of schedule. I submitted the sweater to the Ravellenic Games, earning three medals -- Baby Dressage, Cable Steeplechase, and Sweater Triathlon. Also submitted to Quiddich in the Harry Potter Knit & Crochet House Cup, but not for real points as I'm still a Not-Quite-First-Year. I did complete my sorting form this month, so I hope to have a House and start playing "for real" in September.
Overall I'm very happy with this project, and am really looking forward to giving it to the Lil One for her birthday.