Children
Important special considerations apply to children
For smaller children, buy or make a scaled down mask that fits their smaller face
Other fit issues are the same as for adults
Because children may be less tolerant of discomfort, it is even more important that the mask fits well and is comfortable.
Don't use anything that can become detached from the mask for younger children, because of the choking hazard.
Be mindful that children need to be able to remove masks on their own and that ties may not be a good choice for younger children because of a potential risk of strangulation.