I'd definitely check the hydration status of the animals too...
In the past when I've seen my mice die due to dehydration they have say there and gasped like that.

24 days is the perfect age to wean them; at UC Davis their weaned at 21 days, so you're good there.

To make sure there aren't any extra issues with regard to respiratory diseases, I'd take a 3x5 index card and measure the bottom of the cage with it; the number if index cards it takes I cover the bottom is the number of nice you can maximum house in the cage according to the National Institutes of Health guidelines to prevent excess ammonia buildup in their air. It will also help curb aggression and increase the likelihood of the litters surviving.