With respect, I think any child who is asking a lot of questions about these topics and repeatedly needing reassurance about them is showing some signs of anxiety (which may be mild or not so mild). Others may disagree.
Another avenue would be cognitive behavioral therpay techniques--learning to recognize anxious thoughts, categorize them as the type of nonproductive thought they are, and replace them with a more balanced thought (such as "I know it is very unlikely that an F5 tornado will hit my home" or if you prefer, "We have a family disaster plan and know what to do."). You can Google this and learn the basic concept without a therapist.
