Choose the material you want to make your ear loops out of. Bear in mind that the smaller the wearer, the smaller diameter material you will want to choose. No one wants to wear an uncomfortable mask, so if it's not comfortable on a child, he will be more likely to pull it off.

I found that approximately 10 inches (25 cm) of material is sufficient for each loop, no matter how large the wearer is.

If you are using any kind of round cord, make a tight half-hitch knot in each end to keep it from fraying. This will also help prevent the cord from pulling out of the stitches. Sew one cord firmly to each top corner of the mask. Here, I'm using some leftover clothesline I had from a different project. It's soft and fluffy, but without the knots, it will fray.

With the top secured tightly, sew the bottom loosely. You want the cord to move through the loops, just enough to adjust from person to person, but not while you're wearing it! Sorry to say, this is trial-and-error as you sew. If you're not comfortable with just two or three loops of thread, or if you're comfortable with a sewing machine, you can use some seam binding or piping to create a loop, instead. If the mask is specifically made for one single user, the cord can be knotted below the loop to secure it at the desired size.

Here is the fitted mask I made for my grandson, who is 2. For a cord, I crocheted some cotton yarn(chain 40.) His mom and I felt that the clothesline would be too fat behind his little ears.

That's about it. It took me around 18 hours to do 12 masks, but I was stopping to take pictures (and fiddling with the pattern to get it right) for the first 6 hours. God bless you and keep you safe. Happy sewing! If you have any questions, please ask. I or other experienced needle-crafters will be happy to answer.