I suspect most parents reading this will understand your nervousness—and, of course, you'll want to find out as much as you can about the trip and how it will be organized.
But in my experience almost nothing can be as life-changing for young people as a short-term missions project. For one thing, it helps them realize how most people in the world really live—not in the comfort and security most of us know, but living on the knife-edge of poverty and poor housing and hopelessness every day. The Bible says, "The righteous care about justice for the poor, but the wicked have no such concern" (Proverbs 29:7).
In addition, groups like this can make a real difference in the lives of other people. When you have almost nothing, even a little can make a huge difference. If your son goes with this group, I predict he'll be overwhelmed by how grateful these people will be.
Above all, this can be an opportunity for him to share Christ and His love with people who may not know Him. Often churches like yours link up with mission groups or churches in the other country, giving the participants many opportunities to talk about Christ. Be open to what God wants to do in your son's life, and ask Him to show you His will about this trip.