These types of inquiries will help you understand what the child is thinking while possibly pointing to the underlying fear this belief is covering up.
4. Once you understand a child's beliefs a little bit better, what you want to do is patiently work to replace the implausible explanations with a more rational understanding of death that will provide some the same level of comfort. This is a good time to nurture a discussion about feeling helpless in the face of death, because this is basically what your child is conveying. Say something like...
“It can be scary to think about death. I'm all grown-up, and even I find it difficult to think about on many occasions. But I don't think your get well card had anything to do with it, my dear, although I'm sure grandma was extremely happy to receive it, and it may have even brightened her day so much that she kept fighting a little bit longer. Your grandma died because...”
Then talk about the process of death and help them understand the specifics about how and why it happened.
5. Most of all, since magical beliefs tend to originate out of feelings of helplessness, you should combat these feelings by talking about the things we can control: