Preferred the look of the fabric with a tighter gauge, therefore knitting size 4-6 years to measurements matching an existing jumper that fits which seems to fall somewhere between the 1-2 years and 2-4 years sizes.

Finished measurements (unblocked, blocked):

Chest: 22”, 22”
Sleeve: 8”, 9”
Hem to underarm: 7.5”, 8”
Upper arm: x, 8”