Kevin most likely picked this up at daycare. I am amazed at the way my 19 month old son, Jake imitates his 4 year old brother, Eddie. One of his favorites is to get in a karate type stance with his arms up and his fists clenched, and to let out a loud grunt. Even the facial expressions are the same as Eddies's. He is into so much more at such an earlier age than the older two kids - he has 2 little idols to emulate.
Outside influences enter their lives at such an early age.