Size S best suited for 8-12, Size M best suited for 12-16

Purchased an M to suit myself as a UK 10/12 but felt a size smaller would have been better. For me the M was a little loose around the shoulders so I felt that it was likely to slip off.
Re-ordered in a S and could tell the difference straight away, fits more comfortable across my shoulders and sits comfortably on my bust without flapping around losing visibility of the print. I'm a 34C and would feel that a Small size would be perfect for an 8-12.

My only concern is the tassels, as I know from experience these kind of tassels fray and split in the wash so I would suggest hand wash only. Alternatively if there is a way to singe the ends to avoid fraying I would recommend doing so. Once these start getting tangled and frayed it will really impact the overall look for this Kimono so handle it with care!