Pattern #30 in book.

Sizes and center-back dimensions:
S1: 0-3 months (10.625”)
S2: 6-9 months (11.875”)
S3: 12 months (13”)
S4: 2 years (14.125”)
S5: 4 years (15.375”)
S6: 6 years (16.5”)

Notions:
Sizes 1, 2 and 3: three buttons
Sizes 4, 5 and 6: four buttons