How Baby Shoe Sizing Works
Baby shoe sizes are often grouped by age. For example, you might see shoes for ages "0-6 months" or "6-9 months." While this can be helpful, they are meant to be a starting point in your sizing journey. No two baby's feet are the same (and sometimes your baby's own feet will be slightly different sizes from each other), and there is no universal standard for age-based sizing.
Use age guidelines to pick a size to start with, but the safest choice is to measure your child's foot so that you know exactly what size baby shoes they need.