Okay, so these are a girls size 16 which is equivalent to a size small in women's, but these would also be very cute slightly oversized on an XS.
My best guess is that these would fit a size 0 to 4 best, check the measurements below. Also the straps are adjustable, of course, so that will help with sizing.
Waist laying flat: 15"-15.5"
Inseam: 4"