I would consider the opening introductions of 'He-Man and the Masters of the Universe,' & 'She-Ra the Princess of Power' plus the 'moral of the story' scenes at the end, an obvious breaking of the fourth wall. I recall a scene in the 'MotU' episode: City beneath the Sea, where Man-at-Arms and Prince Adam were sent to investigate the mysterious disappearances of eternian ships at sea, while on board the ship, Adam looks at the camera, then winks and smiles.
At the end of a 'Thundercats' episode, the Thundercats were looking at the camera while a robotic camcorder appears right in front of them, snapping pictures of the viewers (I guess this is somewhat a brief 4th wall breakage)
I would also consider PBS's 'Arthur' cartoon where the title character talks to the viewers just before the the episode begins, to be a fourth wall breaker.