Please explain this to me I’m still lost on this thing.
You take 20 people and put them in a room for 5 hours - all masked.
Halfway thru this time together, they all take of their masks for 30 minutes.
Are they protected from transmission?
Masks don't prevent transmission, they reduce it. So the 30 minutes unmasked doesn't undo the 5 hours masked. And if we are only concerned about lunch, other measures can be put in place to keep kids distanced to reduce the spread.