Get a pair of silly sunglasses. Huge clown ones, silly shape ones - whatever you can find. First you wear them. While wearing them look really hard for a "super singer". The child you choose gets to be the next to look for a "super singer". Sing. Repeat. Sing. Repeat.
*I am not sure if I saw this idea on the Facebook LDS Chorister's Group or on a blog. If you know, please tell me so I can properly credit.