How Often Is Normal for My Kid to Be Home Sick?

Are there any stats on the average number of days that toddlers who are in full-time day care are absent from said day care due to illness?
—Thanks so much for all your amazing work and insights

There are! I wish there were more, since in principle this seems like a pretty easy data set to collect, and the studies we have are not enormous.

But there is one paper that does more or less exactly what you want. This paper, from 1999, uses data from child care centers in Quebec. The researchers estimate that kids miss 2.7% of days. This is higher in the winter months (3.5% versus 2.2%). (They also estimate that kids have a cold on 23.4% of the days, so obviously runny-nose attendance is common.)

I would venture that in the more recent period in the U.S., kids have missed more. This is partly because last fall was awful in terms of stacked respiratory viruses and partly because people have become slightly more conscientious about not sending their child to school a bit sick.