Crochet booties available in 5 sizes and many colors (to order write to me):

0 months (NB): 3,15" / 8 cm / US size 0,5 / EU size 16

0-3 months: 3,54" / 9 cm / US size 1 / EU size 17

3-6 months: 3,94" / 10 cm / US size 2 / EU size 18

6-9 months: 4,33" / 11 cm / US size 3 / EU size 19

9-12 months: 4,72" / 12 cm / US size 4 / EU size 20  

However, it will be better to choose the size of booties according to baby's foot meaurment in cm or inches rather than standard size number according to baby age. Every baby is unique and so the size of booties can be only approximately estimated using baby age number.