I usually prefer to pick one of three ways to ask children to come to the front of the room for an activity:
1. I make a big deal about someone that was really reverent and call them up. I try to do this with the next few children, so that I'm not just choosing children who are suddenly being reverent because they see a reward, but because they are genuinely striving to be reverent and were already being reverent before they realized there was a big "reward."
2. I ask each teacher to choose one reverent child in their class, one at a time.
3. I use the "Helping Hands" jar and choose a name - but I tell the children that if the name I pull belongs to a child that was not reverent, I am putting the name back in the jar.
Our new chorister introduced a fourth way that I am enjoying:
4. She stops in the middle of the song and has children raise their hand if they know the next word of the song. She then chooses a child, and they can go up to the front of the room to participate in the activity.
Some of the younger children don't yet understand that they have to take turns and share, but I rarely cave if they complain that they aren't being chosen. I tell them to try to be really reverent and maybe they'll get a turn. If they really try, I try to give them an opportunity to come up.
If a child waves his or her arms and jumps up and down, I'll eventually remind the class (without drawing attention to the child) that I'm looking for children that are reverently raising their hands.