Shoe sizes run up to size 13 before starting again. at 1....so 1-13, 1-5 with the adult shoe sizes taking over at that point.
The groupings are roughly sizes 1-4 (baby), 4-10 (toddler/pre-schooler), 10-5 ("kid")
The number is what is important and not the name grouping. So if he wears 8/9--shop for 8/9 regardless if they call it toddler or child. HTH!
My son is 3.5 and wears a size 10
My 8yo has crossed over and wears a size 1
My 10yo has crosed over and wears a size 3