Yup, the thing that would concern me is his wheezing. I have a child (of mine) with asthma. When he starts to audibly wheeze, it's almost a guarantee that his oxygen levels are down into the 80's (which is not good).
I would ask mom to get that issue checked out first.
If it was just the cold, there's not much that you can do. Part of the "hazards" of both running a daycare, and having your kids in childcare.