A very young and sweet boy, usually drawn in an anime or manga style. Can be used to describe a boy drawn in a Western style or a real boy too.. although a real shota boy should be over 18, of course.
Comes from the Japanese term shota (itself derived from 'shotacon' or Shotaro Complex), meaning hentai involving young boys. A shota boy, then, literally means a boy who would be suitable for shota, or a boy you would like to see in shota.
"Ed and Al from Full Metal Alchemist, and most of the kids from Young Justice are definately shota boys."