Brothers act like they don't know each other

I work at a child development center. While at work a boy was out in the hallway. The boy's younger brother's class went out in the hallway to use the bathroom. The brothers sat near each other yet did not acknowledge each other at all. The younger brother was crying yet did't even attempt to go to his older brother for comfort. The older brother looked past his younger brother as if he didn't even see him there.

Later on that day, the younger brother was crying again for their mommy. The older brother's teacher allowed him into his class thinking that the boy would settle down because he was with his brother. The older brother continued to play legos while the other children stopped to see why the younger brother. The younger brother stood there crying as if he didn't know his brother at all.... And yes before you ask... I am sure that these boys are brothers.