Life and death

At what age do kids understand about life and death? Is 4 years to early?
The reason I'm asking this is sometime a month ago, Mira woke up at 4 am and asked me where are asteroids and will they come to earth. I told her to go back to sleep and will explain in the morning. After explaining the following day that asteroids are out side earth, she took it fine but I guess it was still on her mind. The following night before bed she was crying saying asteroids might come to earth. We calmed her and after a few days later, she asked few questions.
1. If asteroids were to come to earth, will they hit land , our house or sea.
( My response:IF it does come, it won't hit our house. We are safe. Might land in the sea far far away.)
2. If it landed in the sea, won't  the water splash on us and something might happen to us?( Oops! Yeah but just a splash🤐)
3. Can God see the asteroids coming to earth?( Hmm . Yeah he can)
4. Then why doesn't He stop it?( She's asking me questions on God at 4!! My response was He will stop it from hurting us.. phew)
5. Why can't I see God?( Well luckybi thought about the analogy of how we breathe air but can't see it, but know it's there.)

So my question is - how does this 4 year old wonder so in depth of the Big Picture. Has she time traveled to past or future?

On the same note, my dad showed her a video clip of tsunami in Japan yesterday. After a few hours, my mom found her sobbing thinking about it. Hmmm....