The training and experience I have gained from teaching Primary Music over the years has proved again and again the "MAGIC 7" principle. Young children (and really, even older children and adults) need to hear and experience the song at least seven times before they start recognizing its PATTERNS in RHYTHM, MELODY, and WORDS. Understanding messages and meaning come about much later. These seven first exposures can be simply listening, but even better would include rhythmic movement and something visual to help them with absorption. Only after these seven experiences will they then begin to start participating in the singing. (Just assume that every song is brand new to a young child.)
This has to be one of the most overlooked pieces of the Primary Music Teaching Puzzle. As I have visited many different Primary Music Times across the country, I have noticed the Music Leaders tend to assume that the younger children (mostly nonreaders) will jump right in and start singing as they hold up the flip chart and sing through the song. They think they should. After all, they have already spent 15 of their 20 minutes explaining and going over the words (sometimes to multiple verses in one whack and with no attempts at teaching the notes). "Why don't the kids sing? I taught them the words." Unfortunately, with only five minutes left, the kids may only hear the song played or try to sing it through once or twice. Definitely not the Magic 7 times.
Singing Time ideally should be just that --- a time for mostly SINGING. The song or verses of the songs themselves take mere seconds to actually sing. As a Music Leader, you should be able to sing a song many times through in your 20 minutes. In fact, without a lot of talking, you should be able to sing several songs several times through in 20 minutes!
Talking should be limited to GUIDING THEIR LISTENING. What does that mean? Give short specific demonstrations of how to sing, what words to sing, and possibly provide brief fun activities to keep them interested. These shouldn't be lectures on multiple tasks, just laser-focused pointers --- then SING and do it again with other brief pointers. Keep things moving.
In thinking about all of the things you would like to teach, break those ideas down into tiny parts to fit in between SINGING the verses. REPETITION is the most important thing. That's why well thought out VISUAL AIDS, SINGING GAMES, RHYTHM ACTIVITIES and giving kids TURNS in an organic way (growing seamlessly out of the singing) are so important.
Unfortunately, many complicated games and elaborate visual aids become a distraction away from the real goals of SINGING TIME. If explaining the games, setting up the visual aids, and using "methods" for choosing helpers take up more time than actually singing the songs, they are not worth the effort and expense. Keep to a healthy ratio. SINGING 80% vs. TALKING 20%. Have someone time you sometime to see what you actually do.
Keep to the basics. Having a Bag of Tricks, simple to use and set up Visual Aids and Games, cultivating your own "stage presence," and knowing each child by name are your best tools to find success as a Primary Music Leader. Remember to SING, SING, SING! Watching the children learn many songs by heart AND to love singing is such a joy!