That's a hard question.

Did you try LDSYouthActivities? This is a website where you can ask to be put on the mailing list for information about the Day of Celebration activities. The newsletter is mainly for the Utah area, but you might be able to get ideas from that.

Since your boys sound kind of outdoorsy, you could take a Church History hike. Our ward did this a while back -- they had some hard tack and water for breakfast (they didn't tell the kids this beforehand :lol: ) and the Bishopric led them on a hike where prominent leaders from Church History (ward members dressed up) gave short talks about themselves. The kids loved it, and most of them bore their testimonies about it during Sacrament Meeting--even the boys.