I am only an amateur sociologist, and this answer is not meant to supplant the existing answer(s).
Fear of death is caused by anxiety, specifically fear of separation from loved ones. Put another way, it is fear of (permanent) loss.
In children, the root causes are typically one of:
- personal experience observing injury or death’s impact on people around them
- a little too much truth in advertising about how scary the world can be
In the first instance, children become concerned when those around them become alarmed at things. For example, I have diabetes, and have at times had to go to the hospital. This was rightly stressful for my wife. However, my young daughter does not have context or knowledge to understand what is really happening beyond Daddy is in danger!!!!
It took a while to assure her (even in the hospital but afterwards as well) that I was okay, I wasn’t going to leave her, and I loved her. The simplest explanation, that I was just feeling really bad and the hospital was there to make me feel better, helped her (in reality I was not likely to die unless left untreated for a few days), but only because it was coming from people she trusted. The trauma she felt took a couple of months to leave her. This is normal. What mattered most was treating how she felt.
In the second case, children (as all people) have a basic need to feel safe and loved (antagonistic to fear of death/loss/etc). The trick is that children do not have the ability that we adults often take for granted — the ability to deal with scary stuff, like death and war and mass shootings and creepy clowns hiding in sewers with red balloons.
It has a physiological basis: their brains have not yet developed the ability to distinguish fact from fiction. Things like R.L. Stine’s Goosebumps series do so well because it is age appropriate material for those whose brains just gained the ability to think logically about things and separate fact from fiction. In particular, they are at the age when they begin to learn how to deal with frightening things and (hopefully) overcome many of their fears.
Your daughter is still in the take-it-as-it-is-told-to-her stage, physically unable to really separate fact and fiction.
My recommendations are:
- It is okay to be factual about things (like death), but remember that we first-world denizens have a remarkably safe and healthy lifestyle compared to all past civilizations.
- Remember that fact and fiction are still blurred, so you don’t have to resolve the totality of a doll’s death. The doll’s death is itself fictional, so the doll being ‘alive’ five minutes from now is fine. Your daughter will figure things out herself in just a few years. (Enjoy the fun now. “Oh no! Is she dead again? Can she still play? No? Now she’s sad because she wants to have tea too.”)
- When you (or she, or anyone) does experience injury, don’t minimize it, but don’t blow it out of proportion. A broken arm hurts like hell, but is almost never life-threatening. Remind your daughter that it will be okay, you and she and the doctor (and anyone else even tangentially relevant) are going to get it fixed, and you are always there for her while it still hurts.
- And yes, avoid cynicism. It is not healthy for adults or children. Let your kids become cynical of their own free will when they are older. (And they are less likely to if you avoid it now.) I know this is a hard one to take, because, as adults, we see how unjust the world really is and often feel unfulfilled, unrecognized, etc. Which leads to my last recommendation:
- Enjoy good and uplifting stuff with your daughter; make good memories. Teach her how to explore bushes for cool bugs, climb trees, fold origamis, read stories about princesses saving princes, fix pancakes, and so on. Be happy!
I know this has already gotten a little long, and I’m sure I left out something I thought important, but my wife and daughter are asking me to help decorate the tree right now, so then... I’m off.