Hello,
I don't have a format for letters to generate the interest of the youth. But, here's an idea. Since you all mail out letters to family members, draft a special letter only for the young generation and address the letter to them. In the letter, express how their participation is crucial for the survival of a great tradition. Express that if the young generation are not aware of their family history, they could very well end up "getting with" their own cousin. Also, encourage them that the committee is interested in making the reunion enjoyable for all. Ask them what would constitute a great reunion for them. Hopefully, you will get some feedback.

Maybe others here on the forum can provide a sentence or two on what can be included in this special letter.

What has been the basic itinerary for each of your reunions? When I hear some family reunions have literally "died", I discover that each year, they basically do the same thing...which basically includes everyone sitting around and eating, with little interactions with each other and no fun activities. Then after a while, the reunions grow increasingly boring and people, especially the younger generation, become uninterested.

Include young people on the committee. Set up your programs where mostly young people are doing something. Even try to get a young people to be the motivational speaker. Sometimes, interest may grow when they see other young people taking an interest and getting involved in the planning. My cousin brought up a great idea we are going to try for our next reunion. She is going to set up a "Young Generation" Committee, for them to come up with something they'll like to do for the reunion.

Hope this helps