I overheard my 5-year-old explaining death to my 3-year-old:
Peyton: "Everyone goes to Baby Jesus sometime when they get old. Everyone! Did you know? Even dogs!"
Ella: "Peyton, what old?"
Peyton: "Old is when your skin gets bumpy and wrinkly and has lines. When it gets more and more lines you will die."
Ella: "Yes, you die!"