It's all relative.

Being from Quebec, I spent my childhood recess times outdoors at temperatures down to -15 or -20 Celcius (sub-zero F). However, we were all little Quebecers with lots of appropriate winter gear such as boots, coats, snow pants, mittens, etc. (It probably took about 10 minutes to get us dressed for recess.) Here in Vancouver I wouldn't send the kids out if the temperatures were below 0 Celcius (32F) since most people don't have appropriate winter clothing, and would indeed endanger themselves. I'm not that old (32) but maybe the rules have changed. I sort of doubt it.

If you're in Missouri, I'd sort of expect people to have what it takes to survive the around freezing point.