[A recently retracted study in JAMA Pediatrics] purported to show that wearing face masks was dangerous for children because it increased the amount of carbon dioxide they were breathing into their lungs.
But there were some irredeemable problems with the study. First, the device they used to measure CO2 levels was designed to measure CO2 levels in incubators and had a large margin of error when used in an open setting.
Many researchers who study exposure medicine commented on the paper and questioned whether this device was appropriate. Also, the study measured CO2 levels in the pocket of air inside the face masks of children. But that did not accurately reflect how much CO2 was actually entering their lungs.
[S]omeday, someone might come up to you and claim that masks are dangerous for children… Now you can confidently tell them that that study was actually retracted because it had critical methodological flaws.