Fear of death in children, as well as questions on this topic, is a completely normal phenomenon.
Most likely, the baby is asking those very questions because of this fear, so you shouldn’t make the topic of death taboo.
The correct answer to this question is: "I love you more than anyone in the world, and I want you to be well. But we all - humans and animals - grow old and die. It just won't happen anytime soon."
You shouldn't hide or hush up the fact of death. But visiting a cemetery without necessity is also not recommended. Don't raise the topic of death first, it's better to wait for the child to ask this question.
If your baby is 3-4 years old, then he still thinks in images. Let the answer to this question be figurative: "After death, people go to heaven, sit on clouds and watch us."
With an older child, you can discuss alternative versions.
Just don’t describe the technical details of death in vivid colors – the baby’s fragile psyche is not able to cope with such pictures.