Classic Baby brand raglan baseball top in blues, from American Apparel knits. Has "COWBOY" patch on the chest. 

Marked a boys size 6, but AA runs small so I'd say more a 5/6 (maybe even a big 4 - please check measurements to be sure as it may even be smaller!). 

Chest around armpits is 28" and length from neck to hem is 15".  

Excellent condition from a smoke-free home.