But I made a mistake at the outset. I didn't trust myself. Instead of making the size that most closely matched my daughter's measurements, I made the size that most closely matched her age. Surely at 10 mos., she should be wearing 12 mos. clothing, right? [Since all my kids mostly wear gently used/thrifted clothes I have not found sizing labels to be very reliable. There are times when my 4 yo is wearing size 6 pants, and my baby is wearing 2T onesies.] And since I didn't go with the rational choice, which would have been to knit the sweater that would actually fit her, I wound up with a gorgeous sweater tee, perfectly matching the pattern measurements for 12 mos., but way too big for her little body. She is a petite one, this last daughter of mine, and at 10 months she has an 18" chest, and more closely matches the 3-6 mos. size of the pattern.
I pulled some more yarn from the stash - a lovely reddish-pink left over from the Norwegian cap I knit late last year. And the 3-6 mos. size tee fits her perfectly, with the green one waiting in the wings.