In addition to giving solid instruction in the Confirmation classes, encourage the youth to be active in their Youth Group, and to participate as Altar Servers, readers, and in music ministry. Get them involved on an equal footing with the adults when it comes to service projects - or even let the young people take the lead. Let them feel that they are doing ministry, as well as being ministered to. Let them take an active part in what they do, rather than just being spoon-fed.
Maybe even give them opportunities to give presentations to each other or even to the adults on topics that they like. Most of all, don’t treat them like “kids.” Treat them like human beings who are simply a bit less experienced than the rest of us.