I've tried so many different brands of mask for the adults and kids in our household, and keep coming back to Sock Fancy.
The generous fit prevents it from being pulled down your nose when you talk, and I find this especially important for kids. The adjustable strap is great. Also, based on what I read, the non-woven layer between two cotton layers is one of the best combinations for mask performance. Couldn't be happier with my purchase, and will be buying more.