Just below the lungs, the diaphragm does most of the work that the lungs get credit for. The diaphragm is muscle. The lungs aren’t. When you suck in your gut, it pushes up on the diaphragm, which pushes against the lungs, and —whoosh, out goes the air. Shallow breathing uses very little diaphragm muscle. Deep breathing needs the diaphragm to contract, pulling the lungs open wide to let in air … and then when the diaphragm relaxes(or the gut pushes against it), the air is pushed out.
Singing needs lots of air … so the diaphragm is in constant motion, contracting and expanding to its limits. Warm-ups for singing are like warm-ups for any sport —they get the body ready to work.
However, during Covoid, its helpful to not expel breath(and possibly germs) as exuberantly as usual. Talking, with a mask on, is still alright for music class. Chanting, talking together in a rhythm, using a quiet voice is a way to practice rhythm, beat, following a conductor, reading music and having fun.
So take a look at “One Apple, Two Apples” as a “reading chant. Then try out the “One Zip, Two Zips” to have students substitute their own favourite foods into the chant.
“I Like to Eat” is an incredibly fun song to sing, but the zaniness of changing the vowels works even when spoken/chanted. Check out the pdf material for a way to use this song/chant as practice material for long and short vowel sounds.