Rather than change it to int/ulong, just change it to 'size_t len = parent.children.length+1' (or auto instead of size_t). This way it's proper for both 32-bit and 64-bit and you don't need to worry about architecture. If you do need a signed version, you can use ptrdiff_t.
Yup, that's what I did when my head returned to its usual postion ;=)
