The aunt who was doing most of the childcare on Friday is a teacher so it's possible they discussed it around him, but I don't think he's able to understand that sort of thing at all. He talks vaguely about "bad guys," lumping "zombies" and "creepers" and other fictional baddies together (thanks, cousins who are older than him) and discusses "shooting" them but he really doesn't have a handle on death AT ALL. He's still at that stage where death/dying is a physical going someplace else. he also talks about going to the rocket ship store to buy a rocket ship to travel to the real earth so he can be in it (what?) instead of simply on it as we are now. He just... he's 3. The world is kind of baffling in many ways.