From the Knit Picks Website:
Get ready for fun in the sun with this slip over dress in easy care cotton; simple for beginners and adorable for all girls in sizes from 3 months to 12 years!

Sizes:
3-6 months - 20” chest
12 months - 21” chest
18 months - 22” chest
2T - 23” chest
3T - 4T - 24”-25 chest
5T - 26” chest
6 - 27” chest
6X - 7/8 - 28”-29” chest
10/12 - 30” chest

Needles:
Size 3 (3.25mm): 24” or longer and 16” circulars