It can be so confusing buying shoes for your little one!
They don't "need" shoes until they start walking, even then as much bare foot time as possible is ideal. When they start running about and have established walking (around 24 months of age) they are ready to move to a hard sole.
Baby shoe sizes start out at 10.5 cm which is generally good for infants 0-6 months, we call these 'pram shoes' as they are just for show :) They then go all the way up to 17cm which is good for children 3-4 years of age. Once a child is 3-4 their shoe size becomes a little easier and they fall into the junior sizes (10 upwards).
At 4.5 Sienna was in a size 11, at 19 months Stella fit our 12-18 month sizes.
We currently offer "early walker" sizes:
6-12 months, Size 3 (11.8cm)
12-18 months, Size 4 (12.6cm)
Our new walker and childrens shoes will be out in December 2017, stay tuned!