5.4-ounce, 100% cotton tee. The XS is comparable to a 4-6 kids size.
KIDS You Never Can Tell Tee
All of these shirts hold true to size after washing. If they are 100% cotton, they will be slightly bigger before washing but come out as expected.
Here's how the kids sizes translate to age, generally:
XS = 4, S = 6-8, M = 10-12, L = 14-16, XL = 18-20