Die..accident....does little Grace really understand the meaning?

I had always try to explain to Grace what does die means. You see, this little girl is much too active sometime, even when she's in the car. Now, sitting in car seat is not really compulsory in Malaysia. We only had one car seat which is on my car, so that I can fetch Grace along when I'm driving alone. Thus there's no car seat in daddy's car. Whenever we're in daddy's car or someone else car, I had a hard time making sure that Grace is safe. With her climbing up and down, it is really a hard and tedious.

As such, we will tell her why she had to sit still, be quiet and buckle up in the car. Explained to her what will happen if there's emergency break or if there's an accident. We told her the worst case will be she being thrown out of the cars and it will hurt very much and she might die. We will tell her, then she will not be able to see mummy already. She will node her head, and say that she don't want to die.

Then here's 4 situations on how she uses accident and die:

Situation 1
Grace: Mummy have to drive carefully. If not, there will be accident and will die. Then cannot see mummy already.
Hmmm......not bad.

Situation 2
We were at Cameron Highlands and was heading to the tea plantation. The roads there are steep and narrow. Daddy has to be extremely careful. So we told Grace to sit quietly so as not to disturb daddy driving, thus avoiding accident. Then along the way, this is what Grace said.
Grace: Mummy, 有 "a-si-dent" (accident) 吗? (有 pronounced as "you" and 吗 pronounced as "ma", meaning Is there accident?)
Oh my, oh my.

Situation 3
We were talking and all of sudden, Grace said this:
Grace: 我不会死的。 Mummy 才能死。 (pronounced "wo bu hui si de. Mummy cai neng si", meaning I won't or can't die, only mummy can die.)
Mummy: Speechless........?!?

Situation 4
We were cuddling up in our bed. Then I climb over her and pretend to press down on her.
Grace: Mummy 不要这样。这样我会死的。 (pronounced "Mummy bu yao zhe yang. zhe yang wo hui si de" means Mummy, don't do that. If you do that, I will die.)
Mummy: Speechless again...............