Would you consider someone as childish if they were nervous/frightened during a storm?

Your comfort level during a storm is directly related to your knowledge and understanding of them. If you don't know much about then you'd be wise to be fearful. If you know all there is to know, what precautions you need to take and when you need to take them etc, there's a lot less to be afraid of. To the best of my knowledge nobody has ever been born yet with all that knowledge built in as standard issue.