You weren't necessarily bad parents; in fact, I suspect you were actually very good parents. And you certainly had worthy goals for your children; unlike you, many parents never stop to think about what kind of people they want their children to be when they are adults. But this wasn't true of you.
In reality, as parents all we can do is provide the best possible moral and spiritual teaching for our children -- both by our words and our example. But our children aren't computers; we can't program them to do exactly what we want them to. They alone are responsible for their decisions, and they alone are accountable to God for how they respond to what we've tried to teach them. The Bible says, "The son will not share the guilt of the father, nor will the father share the guilt of the son" (Ezekiel 18:20).
In other words, don't be weighed down by a burden of false guilt -- that is, by guilt you don't deserve to have. If you know of areas where you failed, seek God's forgiveness for them -- and also the forgiveness of your children. But they alone are responsible for the path they've chosen.
At the same time, pray for your children, and let them know you still love them, even if they haven't followed the path you hoped they'd take. And don't be surprised if some day God moves in their hearts and draws them to Himself in repentance and faith.