College is a very typical time for young adults to fall away from the church because they don't have their parents getting them up in the morning, have their friends waiting to see them, or feel comfortable among strangers. Also, they may not have easy access to a church as not all students head to college with a car or may be a bit shy about trying to round up a ride or invite a friend with a car to go to church with them. None of this means they have lost their faith or will not eventually go back to church once they're done with college or begin establishing a stable life, getting married, having children, etc. It is actually an important time because these are the years where they choose what activities their life will include. They are setting their priorities.
If this is a concern for the parents I offer up a suggestion: When you drop them off at college for their freshman year be sure that you're there on a Sunday so you can go to a close, local church together, meet the pastor, perhaps a few young people, stay for an appropriate Bible study and help your child become comfortable there. Ask if it is possible that somebody could give them a ride on Sundays.