The following are general guidelines for average infant/toddler shoe sizing:

Size 1: Fits a baby 6-12 weeks old.
Size 2: Fits a baby 3-6 months old.
Size 3: Fits a baby 6-9 months old.
Size 4: Fits a baby 9-12 months old.
Size 5: Fits a toddler 1 to 1-1/2 years old.
Size 6: Fits a toddler 1-1/2 to 2 years old.
Size 7: Fits a toddler 2 to 2-1/2 years old.