One study I read stated that around 23% of young people suffer from at least one mental disorder or disease. Another thing that's hard to control is who your children hang out with. In their teen years they are at home less and less, so your influence becomes less and less as well.
One thing that greatly increases the chances that your children will have good influences around, is to enroll them in programs (i.e. band, clubs, sports, etc.). Countless research shows the positive impact these programs can have on the future lives of those who participate. The fact is, very few people are in prison who used to be in band. Most of the good students in school are in band. A coincidence? I guess to scare you straight, I wasn't in band and look what happened to me! :)
A shout out again to all parents. You amaze me and I'm so thankful for your sacrifices. Children are our future and you shape them!