|image from LDS.org|
Make 8x10 pictures of either words or pictures that represent words or phrases of the song. Have the children come up and hold the pictures. After singing the song approx. 3-5, have all the children close their eyes and take away 1-2 pictures away...have those children that were holding the pictures sit down and then have the children open their eyes and sing the song without those pictures. Do this until all picture helps are taken down. Repeatedly tell the kids how smart they are and then tell them you're trying to stump them. Reverse psychology :) ...the kids love it.
*Tip from my awesomely talented Mother-in-Law, Charlotte Stott Coleman who has been a Primary Chorister many times