Depends on what country of sizing you want to convert it to but in general US 24 = Australasia = 6 / UK = 4 European = 32 and US = XS which is can be between 00-2 depends on the manufacturer as sizes...
There isnt one. Shoes are made in progressive sizes so a womens size 9 does not have an equiverlent in a child size - it goes baby to girl to women in size and males have baby to boy to man