It’s important to remember that COVID-19 is a new virus. It poses new challenges and requires new solutions. Because of this novelty, we will not be able to point you to exhaustive safety studies that have been conducted. We can tell you that for the vast majority of the general public, including children over age five, there have been no observed health risks when wearing a cloth face covering even for extended period of time. The use of face coverings does not lead to CO2 intoxication or oxygen deficiency.
Children and youth five or older have been wearing them in child care, preschools, and day camps for several months without incident and experience in countries where mask-wearing is more common, has not indicated any safety concerns.
Those who are younger than the age of two, those with certain medical conditions, and those who are not able to remove the face covering on their own should not wear one. Masks for children ages three and four are optional and require adult supervision.