This is a standard fit kid's t-shirt set out in age ranges. Please note that size 12-14 fits U.K. women who are size 8!
How to measure your child or teen's chest:
Stand them up straight with their arms hanging down in a relaxed, natural pose. Measure around the fullest part of their chest. Tight up under the armpits and over the shoulder blades. Make sure the tape is flat across the back.