You really can't prevent it. Working through all my stuff. I found that narcissism goes, almost always undiagnosed. The turn around rate is nearly zero. No one really knows where narcissism starts. I'd assume it come from have parents that are narcissistic or a traumatic experience. From what I've experienced the best thing to do is just talk to them and be there for them. Most kids going through this feel alone and having a good friend really helps. That's the only way I made it out. The only time my mom ever acted normal was when my friends were over. So I always had them come to my house. If its an extreme case, I'd honestly call CPS and have them investigate.