Many of you have heard me talk about this before, but I can't stress it enough. The key to a college student's spiritual walk in college is directly tied to their participation in a campus ministry like Campus Crusade, InterVarsity or Navigators or in a good church. In my experience with students, the campus ministry is the "gateway" to a good church in college.
If your kids are in college, do all you can to get them involved. I know, it may be impossible to force it at this point if they don't do it on their own, but it might be worth nagging about, calling a vibrant ministry on campus and asking them to target your child, offering financial incentives or disincentives to your child...whatever is not sin and will work for YOUR child is worth trying.
If your child was involved in our student ministries, chances are they will seek it out for themselves, but they may need a nudge. One of ours knew how important it was, heard Tim and his parents (us) talk about it all the time and fully intended to join, but school was busy and starting new things is intimidating, so he put it off. With some nudging and nagging and praying and a phone call to the campus ministry, he got involved and is a leader in that ministry today.
The other side of all this is that after you've done your part and exhausted your options, you do have to let it go and hand it over to God. Keep praying, but stressing out about it won't help anyone.
But in my experience, parents let go on this way too soon. Sadly, some let it go as early as junior high. If you required your kids to go to school and to work and to get good grades but did not very strongly urge or "require" that they go to church or student ministries of some kind, repent now. Yes, there are exceptions to this, that's why I make it a habit not to judge any persons situation (I'm not walking in their shoes), but chances are you're not one of those exceptions. Repent now before it's too late to make a difference. As long as they are your dependent, it's never too late to start "requiring" that they also cultivate this value that far surpasses good grades, a great career and a good work ethic in importance.