What a nice thread you started!
Right now I am struggling because both of my children have turned away from God. I raised them in the church. They never missed church or Sunday School and the lessons were loving and caring, not vindictive or scary. But they have rejected it all. I feel like I have not been a good enough Christian example to have them turn away so completely. I think if I had been more cheerful, not had so many problems, had things go more smoothly, it would have strengthened their faith instead of losing their faith.
My favorite verse is II Corinthians 4:8 "We are often troubled but not crushed; sometimes in doubt, but never in despair. We have many enemies but are never without a friend, and though badly hurt at times, we are not destroyed."
From a self-proclaimed BuddhiPagaChristiaTotemist (or as Gonzo from the Muppets used to say, "A Whatever"), I'm sorry you are going through this.
I think all children eventually separate from what their parents believe, at least in the beginning. Belief ebbs and flows a lot when people are young, and what we've learned in childhood needs to be proven out by our own experiences as young adults, and then just plain adults.
I think it's also important to remember that your relationship with God is not going to be the same as your childrens', just as their relationship with you is different from all the other people they will meet along the way. You gave them a foundation, but now is their time to decide what that relationship will be.
I know more than my fair share of "wild child" friends who it seemed would be the furthest people from religion their entire lives. Drugs, trouble with the law, everything you could think of. These days, now in our 30's, most of those people are usually some of the most devout and faithful people I know. And all of them, in their hearts, are good people.