Ever since I read Rosencrants and Guildenstern are Dead I've been pondering this question.
In the book, one of the characters theorizes that since he cannot recall a single event that would give him the awareness of death, people must be inherently born with this perception of mortality. I sort of agree because I can't remember anything that would make me realize I can die.
But if you look at a little kid, they do stuff that clearly shows they dont know they can die. My little sister climbs places, puts small toys in her mouth that can easily get lodged in her throat, plays with knifes. We of course punish her for these things, but she does them anyway because she doesn't know any better.
This makes me think it's the things we see as we grow up, especially on TV, that make us aware. For example, when many people first saw Lion King at a young age, they cried when whats-his-names father fell off the cliff. The perception of death was not deeply imbedded in our mind and hence it was traumatical, I think. As you grow up, you become accustomed to the presence of mortality, ie. you see death in the news every day and it's a mere "That's terrible" followed by a click on the remote to switch the channel.
What do you guys think?