Sizing is sometimes a problem so here are some notes which might help.
There is always cross over with sizing particularly with children's sizes and if you can find out the child's shoe size, that is best.
However, here's a rough guide to UK sizing.
Size 6-11 is generally a man's size.
Size 6-9 is a man's style but will not be big enough to fit up to size 11.
Size 4-7 a ladies or early teenager.
Size 00 is newborn.
Size 0 - 2 1/2 is a baby size.
Size 3 - 5 1/2 is probably 18 months - two and a half.
Size 6 - 8 1/2 up to about 4 years.
Size 9-12 around 4 - 6
Size 12 1/2 - 3 1/2 - 7 - 9
Many children now have quite large feet and can from aged 10 (and in some cases, younger) need size 4-7.
I hope that helps but please let me know if we can be for further help. email on firstname.lastname@example.org or call us on 01671 404043