Cut your main fabric like the photo below. If you fold it in half, the dimensions are approximately 12" across the top (24" total width), 4" along the sides, and 14" down the centerline toward the point. Reduce the length and width a few inches for a kids sized face mask.
I wanted to use up some fabric I had so I put two pieces together, otherwise there is not a seam in the point that you see in the photo.
Cut a piece of fleece the same size.
Lay out two strips of velcro so that you can see exactly where you need to sew them. Sew on the velcro pieces keeping in mind that you need about 1/4" on each edge for your hem.
Sew on your velcro to the front of each piece. Then take your two pieces and place them front to front and sew 1/4" around each edge, leaving about 2-3" to turn the piece inside out.
Once the piece is turned right side out and you have sewed up the hole, I do some decorative stitching as shown below.
Now it's complete and ready to wear on those chilly days snowboarding, skiing, biking, or anything else!