For Sam (11 months old now) I made a 12-18 month size. I shortened the sleeves and hemmed the skirt to where I wanted it. Actually I didn't measure, just ironed an approximately even distance all the way around, folded the raw end into the hem, and stitched it around. That's how I do hems. Hope for the best and plow forwards.
She'll be able to wear it for a while, which I consider a bonus. It has buttons, which caught me off guard since this is a knit pattern (fabric from Wanderlust fabrics), but the buttonhole making practice was good for me and of course it turned out just fine, it's an Oliver + S pattern! They always work out.
For Abby's I sewed up the size 5 and it's clearly a little large in the shoulders. I used the bottom of one of my old shirts that became too short after I disregarded the washing instructions...oops. It has a bit of a hi-lo hem that I like.
I can also see this one transitioning into a tunic really well when she gets taller, so that's another bonus. The mustard was from Girl Charlee a while back, and is thicker than is probably ideal for this, or at least for the thin jersey that I used for the skirt, but that's alright.
There's also cool facing instructions that give the neckline and buttonhole parts some strength, and I found the topstitching templates great as well. I always learn something new with these patterns and they ALWAYS turn out looking really well done.
Abby's already worn hers a handful of times since I finished it, so that's a win despite it's imperfections!