Excellent question Josie! This is something I have had to deal with for all of my children's lives. When they were young, the question was what to tell them about my mental illness... the depression, PTSD, SI & multiple hospitalizations. I never lied to my children about what was going on. What I did tell them was dependent on their age and level of understanding. When they asked specific questions I answered honestly. The subject was approached according to their needs. Kids notice everything and the worst thing you an do is lie to them about the obvious. That just teaches them to not trust their own instincts and understanding.
Finally, there is no way to keep them from going down the same road. The best way to try...was to get my own act together to the best of my abilities. Education is important too, whether it be about mental illness or addictions. Just being open and honest seemed to work well with my children. They are grown and on their own now... living productive lives... and seem to hold little resentment towards me about their upbringing. I'm so proud of them! Happily, they are proud of me too.