Post surgery crop for kids

My 11 year old Daughter is having open heart surgery in 2 weeks time 😔
She is quite developed and the doctor has suggested we buy her some zip up front bras for post surgery as she’s not comfortable wearing nothing. She is very thin and the smallest Ladies crop we can find is an 8 which is still too big but I’m struggling to find anything in kids sizes. Would anyone have any suggestions on where to find something small enough? We live regional so it would have to be a store online.
Thank you in advance x