See below. Identify things you can control and deal with that. Work on letting go and acceptance of things you cannot control. Psychotherapy might help you guide through the process. Identifying thoughts and situation that are leading to that fear will also be helpful.
CBT. Seek a cognitive-behavioral therapist who specializes in phobias. One method they use is systematic desensitization which slowly and incrementally brings the person closer and closer to the thing they are afraid of in slow, graduated steps that help make the anxiety more tolerable.
Let go of anxiety. Not knowing the child's age, it seems most reasonable to accept that you cannot live your child's life. You give them guidance as they grow up, be a good listener, and then let go (i suspect that this is a young adult at least in question). If it is really serious risk taking, suggesting some outside help (in a gentle nonjudgmental way) is your best bet.
Psychotherapy. Identify your thought processes and bodily sx. Even if you're not mad, your body still experiencing something. Find a mental health professional to help you through the process. Consider medication if there's a need.
How do I get over my irrational fear of losing control even when im not the one at risk, my elderly parent is?
Losing control. Is the "risk" one of actually losing control or just being afraid of losing control. Watching an elderly parent fail slowly over time does tend to make one very aware of control issues, as there is basically no control over this. Is your parent "afraid" or just you? At the heart of most of these control issues is a fear of death and disease that we usually don't want to think about. Talk about it.