Having grown up in Minnesota, come late January and early February, on the days when the high temperatures are under 0F/-18 C, putting a child out there for 8 h

Having grown up in Minnesota, come late January and early February, on the days when the high temperatures are under 0F/-18 C, putting a child out there for 8 hours under a radiant heater, I think you might actually melt hats/coat hoods before you fully prevent frostbitten toes. Even if you can keep the whole kid at reasonable temperatures, I think it would just be very distracting. Also, for that power/propane bill, you're probably better off with either per-desk transparent positive-pressure medical isolation tents or full-face snorkel masks fitted with 3D printed adapters to ceramic-element anesthesia machine air filters. In addition, kids play. Some small percentage of those kids are going to get burned by heaters.