He told Westwood One Radio that the scandal shows that Americans' first priority needs to be protecting kids.
The president added that when people see someone mistreated, it's their responsibility to step up and take responsibility - and not rely on bureaucracy.
The Penn State scandal has cost football coach Joe Paterno his job. He was faulted for not alerting police after he was told about sex abuse by a former assistant coach.
Obama spoke on the deck of an aircraft carrier at halftime of a college basketball game.