I hadn't given much consideration to making masks for children, maybe it is because my own children are both young adults.
I am a research nut, and most children fall in the least impacted demographic, but are also most likely to be carriers for the virus and pass it on to adults and others in the vulnerable groups (which are estimated to make up 33% of the US population). [Source Kaiser Family Foundation]
This lower impact higher risk of spreading really does put children in a group that needs to wear masks when out in public or in situations where social distancing isn't possible. I know this is why schools remain closed and why my own son isn't getting a proper graduation or senior prom.
There are things you should know about masks and children. Just like you, their mask needs to be well fitted to their face, they need to learn to not touch the mask and how to put a mask on and take it off safely.
Most kids are going to resist wearing a mask, they aren't particularly comfortable for adults and even less so for children. One of the best ways is to lead by example and show them how to properly wear and remove a mask numerous times as practice.
Consider making it a challenge, start by trying to see who can wear their mask the longest and offer up something they might enjoy if they win (like a favorite snack or meal, or playing a game as a family).
Take it as an opportunity to teach your children about social responsibility. Tell them about who is most at risk, how people can be sick with the virus and not know it, and then ask them who they think they know that would benefit from their (your child's) wearing of a mask. Use this moment to teach them about love for other people. And each time you must take your kids out of the house, have them pick someone they love to wear the mask for that day. Children are more likely to wear their mask if they know it is helping to make a difference in the lives of other people.
Ask your children what would make it easier for them to wear the mask - kids are full of great ideas (and sometimes funny ones) and this is the perfect opportunity to engage them in creative thinking that is goal oriented.
You should never put a mask on a child that is under the age of 3. They do not have the coordination to safely remove it themselves nor do many under the age of 3 have the ability to let you know it is uncomfortable or if they are having issues breathing. It also poses a real risk of strangulation or suffocation for this age group.