Q:

How much time should be spent on vocal warm ups for children's choir?

How much time should be spent on vocal warm ups for children's choir, aged 9 - 13, in a 30 minutes lesson?

A:

This is a question where even professional choir directors and singers can't agree on. Some do quite long vocal excersises (sometimes with all kinds of gymnastics) and some just start to sing.
The excersises are not so much about not wrecking voices but more about getting in the right set of mind for reheasing and 'tuning' your vocal 'instrument'. It allows to leave the busy world on the other side of the door.
If a singer has a bad technique then the warming up excersises won't help him/her not to wreck his/her voice.
I prefer a short warming up period (no more than 5mins) to get into the spirit of the rehearsal. But as you have only 30 minutes with the kids, I would suggest to start with a known song or to teach them a special song for warming up.
When you use a known song, they can look at you all the time instead of their scores and you can then sign them to sing louder, softer, faster, slower,...
That way you'll teach them to follow the conductor, get them in the right set of mind for the rehearsel, keep it fun for them and combine warming up with another excersise.

