What size chest is the child? Mum usually buys my clothes bigger than I need. If she is tall and thin then you may need a small boys rather than the extra small one. Also if you get a bigger shirt it can be worn over a jumper for when it's cold. Chest Size Waist Size Order Size 22/24" 22/24" XXXS 26/28" 24/26" XXS 30/32" 28/30" XS 34/36" 30/32" S