Next we had a trivia game where the kids all had to use their hymnbooks to find the answers....questions like when was this hymnbook published, who compiled the first hymnbook, how many sections are the hymns divided into, how many hymns did so-and-so write...all questions they can find answers to in the hymnbook. I made sure to make questions that would have them look in each section, like the tune names, scripture references, authors, etc. We reviewed the answers together as a group and everyone (regardless of how many answers they got right) was given Smarties candies and Dum-dum lollipops.
Then we had a name that tune game, with two volunteers, one saying they can name that hymn in so many notes, the other trying to best him or saying "Name that hymn" and then a kid from the audience would secretly tell the pianist what hymn to use, but it had to be a common hymn, one that everyone would know. The kids loved this game. After each round two new people would go up. If neither of the two could guess, it was opened up to the audience. The prizes got better with this game, under the impression that the 'greater your knowledge, the greater your reward.'
The last activity was a harder trivia game where you couldn't use hymnbooks. I placed an object at the center of a table that everyone who wanted to participate gathered around. After I asked the question and said "Go" whoever grabbed the object first and got the answer right won a prize. These prizes were the best ones, so if you won one of these, you were 'out.' These questions were like "What song did John Taylor sing to Joseph Smith in Carthage Jail?" or "True or False, Gordon B. Hinckely wrote onf of they hymns in our hymnal."
For refreshments we had green cookies and milk. I think the kids liked the activity and understood that a knowledge of the hymns and conducting would be useful to them throughout their lives.
--On a side note, the prizes I gave out I got as a donation from one of our local radio stations. I asked if they had anything they would be willing to donate (morally clean!) for prizes for a church activity (I had previously discovered that they often consider this type of thing a "charity donation.") It was exciting because they gave us beanies (which were the kids favorites), cds, perfume samples, lip-gloss rings, origami books, dvds etc. The only tricky part is making sure that it is fair for everyone who participates in the activity. That's why I tried to make sure that the harder the activity or 'knowledge' they higher the prize (like the cds). If this is okay with your leaders and/or bishopric, I highly suggest trying to seek this route with prizes, because it costs nothing and the kids were so excited about the prizes.