Anyway, I've been anxious to post this idea I used a few weeks back. It worked surprisingly well!
We had learned the verses to Families are together forever the previous week. So, this week, I reminded them about the song we had learned about "families". Then I brought out a family of "little people". I had a Dad, Mom, Brother, Sister, and Baby.
I told the kids to look at them very carefully. After a few seconds, I covered them up, and we sang through one of the verses. 
When we finished singing, I took away one of the figures (all still covered up), then had them guess which one I took. They had no problems figuring it out.
When we finished singing, I took away one of the figures (all still covered up), then had them guess which one I took. They had no problems figuring it out.
but then...
we added the family "pets".
For junior primary I added them two at a time. For Senior primary, I just stuck them all out at once. After adding the figures, we'd cover them up, sing a verse, then I'd call a volunteer to take one away, then they'd guess which one was missing.
We played this Over and over and over, so they didn't notice how many times we sang through the verses! At the end, I told them I was going to try to make it harder, by having the sing BOTH verses...giving them more time to forget! They loved the challenge. My own kids begged to play the game when we got home from church.
Can you tell which one is missing?
When I do this again, I plan on bringing in "extended" family, i.e. aunts, uncles, cousins, etc! :)