My uncle's child is ill. What should I say when I call my uncle?

If it is serious, you must tell your guardian at once. You should be nervous. Apologize first. Then, simply tell him what happened and the current situation, and ask the suggestions of the parties. If it's not serious, tell him, but you'd better relax. I suggest that you don't tell him if it's really okay, and you don't report bad news.