Health visitors recommend having your child’s feet measured a few months after they start walking. They advise that at this point they need good fitting shoes to aid them in learning to walk and support their ankles.
After this first measurement there are not many guidelines as to when you should measure them again, but ideally at least once a year. I recently took my little girl to have her feet measured and she was showing as a 9.5. I felt that it would be better to get her a size 10 as not all shops do half sizes and surely it was better for her shoes to be slightly too big than too small. When it comes to buying new shoes for children, it is essential to get them to try them on (although this can be a battle) as they will often fit differently depending on the width etc.