Here are several more ideas I thought of for "redirecting" the attention of the kids back to you.
Tell a riddle. Say "I'm going to give you some clues to a riddle. Can you guess who (or what) I'm talking about? That's right. We're talking about that today. We know a different song about this. Let's sing..." Some people are good at doing this kind of thing off the cuff. If you aren't one of them you can practice doing it ahead of time. Or, you could prepare a few riddles on slips of paper and keep them in a small can or basket to draw from when needed.
Begin humming a song. See if the children can guess the song. Then carry on with what you were doing.
Show the children a scarf, feather, paper snowflake or something similar that quietly floats to the floor. Say, "I'm going to drop this feather. Before it hits the floor would you all try to think of one way you can be reverent?" Ask for an idea and then say, "That's a good idea. Let's all fold our arms (or smile, or keep our feet still, etc.) while we sing..." You could expand this idea into a full singing time if you wish, by continuing to take ideas and singing reverence songs.
Keep a "secret picture" on hand. One related to the song you are currently teaching, or a general picture of Jesus or a reverent child. Put it in an envelope. If the children become restless, stop and say "I have a secret picture. Joseph, would you like to see it? Would you show it to everyone?" After everyone has seen it, make a brief comment about what you like about the picture, then return to your presentation.
Keep a large, medium and small sized button nearby. When you need to redirect attention show the large button and ask them to listen to hear it hit the floor or the table. Ask if it makes a big sound? Ask them if they can hear the medium sized button and then the small button. Use other small objects on different weeks.
This is an idea adapted from the Sunbeam manual. Cup your hands in front of your mouth and begin to blow, as if you are blowing up a balloon. Let your hands and then your arms spread out into a big circle in front of you and then over your head. Then make a shushing sound as you let all the air out of the imaginary balloon and gradually bring your hands down into your lap. Don't explain anything to the children, just let them watch you. The little ones will copy you right away. If your singing time is combined, count on the bigger boys being silly. Tell them that the balloon has to stay in the chair.
"Clap your hands, clap your hands, clap them just like me." Softly clap your hands as you chant and then change and clap them on your shoulders, knees, head, etc. This works really well with the Jr. Primary. You can find the longer version with actions to touch your shoulders, tap your knees, and shake your head in the Primary 1 manual on page 55. If your Primary is combined, it can work with the Seniors also, but you may have to increase the difficulty of the motions. Look for two more activity verses on pages 127 and 128.
Some choristers have a "church mouse" small enough to keep in a pocket. If things get out of hand the church mouse peeks out enough for the children to see and then hides again. The chorister explains that the mouse is very shy, but loves to hear children singing. Tell the children that maybe this shy mouse will come out to listen if they sing more reverently and do not scare her away.
I think one could adapt the story "Primary Manners" from the December 2009 issue of The Friend into a great singing time focusing on reverence. I would just use the chalkboard illustrations, maybe drawing them for the children and asking for their ideas and singing an appropriate reverence song after the ideas.
Some of these ideas are adapted from the Primary 1 manual. There are a number of activity verses and suggestions for wiggly children in there. The Primary 2 and 3 manuals also have ideas. Don't be put off by the age designation. If you study these books with a little imagination you'll think of ways to adapt the suggestions for the older kids. Activity verses are really good to give the children a little rest and get them moving a bit. Everyone can participate! I think this is why the activity songs are always so popular with the kids. They like to move!