1. They run into a problem with children being reverent.
2. Their primary presidency is hogging their Singing Time.
I've addressed #1 in this post, but wanted to make a comment on #2.
I served as the primary chorister through three primary programs, and am now serving as the primary president. When I was the primary chorister, our children had all of the songs memorized and sang them beautifully, with dynamics and even some sign language, in the program. I believe this will happen this year with our new chorister.
I feel this was able to happen (and will continue to happen) because:
1. The primary presidency worked with me as a team. We supported each other and loved each other, and that love and respect helped bring the spirit into the room.
2. We respected each others' times. Per the official church Handbook 2, Singing Time should be about 20 minutes, and Sharing Time should be about 15 minutes. Notice the word "about!"
Often times Opening Exercises ran late. If this happened, I would take my Singing Time a few minutes over into Sharing Time to split the difference. Sometimes, the primary president or a counselor would just let me know that I could use up even more of her time. Other times, if they were running a little behind (which is often because sacrament runs late) but had a particularly complicated lesson, they would just let me know that they wanted to make sure to get their full 15 minutes. I rarely had more than 15 minutes in Junior Primary, but the presidency rarely had more than 10 minutes, too; it was just the complexity of Junior Primary.
3. We had Singing Time first, then Sharing Time, which helped to keep us on our toes with the schedules. In other words, if the presidency was behind, they could see that it put me behind schedule, and in turn, I could evaluate and see where to split the difference to get a fair amount of time without impeding their ability to teach an important gospel lesson.
The church would not have both a Sharing Time AND a Singing Time if they didn't feel that it was important. If your primary presidency is being too casual about opening exercises, and then taking a long Sharing Time, then talk to your president about your concerns. Pray for guidance on how to best handle the situation. You are on the same team, your Heavenly Father's, and this is Heavenly Father's primary, not yours. You both have the same goal to teach the children the gospel and to let them know how much they are loved! Both you and the primary presidency are trying their best with the current callings and if you are fighting and don't try to work it out between yourselves, you will both lose by driving the spirit from the room as you feel resentful toward each other.
What I posted on the message board:
I would recommend both the presidency and the music leader read and review Section 11.4.2 of Handbook 2 (https://www.lds.org/.../handbook-2.../primary...). Singing Time should be about 20 mins. Sharing Time should be about 15 mins. I have been both Primary Chorister and Primary President so I have experienced both sides. In both situations, we have been respectful of each others' time, which is to say, that sometimes one of us went over a bit, but we were and are both trying. Some weeks skew a little more toward extra Singing Time, and some weeks skew a little more toward Sharing Time, but generally, we follow the 20/15 split. You need to make sure your concerns are understood and recognized before you start to go down the path of feeling resentful or escalating. The primary presidency may for some reason not know, or may be overwhelmed if they are new, or, I hate to think this - but for some ridiculous reason simply not understand the value of teaching the gospel through music. You want the children to feel the spirit in the room as you teach, which means you and your primary presidency need to be a team and have good feelings toward each other. You all have the same goal! Good luck.