"AMEN" is good, but any phrase from a gospel song will do, like "I am Souled Out" played in different keys...melody is good, parts better. Some do vocalises (the ah-eh-ee-oh-oo type exercises) and tongue twisters to get the vowels and consonents under control.
Also I have the adults stretch and move about, and the kids jump about before we do a phrase from a song I want them to learn...