Patagonia blue/dark-blue striped Capilene crew baselayer. Size M (10). Has a couple pulls - shown in last picture. $35 Retail.
Website states: The Kids’ Capilene® Crew is our most versatile baselayer, made of a soft, comfortable polyester/spandex fabric blend that stretches, wicks moisture, is quick to dry and has HeiQ® Fresh durable odor control. Slim fit. Fair Trade Certified™ sewn.