After that it's time for a gentle vocal warm-up. Check breathing - relax your tummy muscles outwards as you take a breath in. These exercises will insure properly warmed-up voices. You can do this by drinking plenty of liquids throughout the day. Be sure your students do this as well.
Alcohol is also bad for the voice, as it dehydrates the body and therefore the vocal folds.
It will make you and your students feel calmer and more confident. After speaking for a long time, warm-down by drinking some tepid water. Yawn and then breathe deeply. A yawn is a good exercise for your kids singing as well. To nurse your voice through a cold or a throat infection, steam it - put some hot water in a basin, lean over it gently with a towel over your head and inhale the steam.