Since the stay at home order was issued in Illinois, I've been working remotely. Luckily, my home office is right next to the window. As I look outside, I'm seeing more and more kids riding their bikes. Most of the younger kids are wearing helmets, many of the older ones are not.
Everyone and I mean everyone (little kids, big kids, teenagers AND parents) should be wearing one when they're riding. They are a really important safety device and can prevent brain injury in many crashes and falls.
We want everyone wearing a helmet AND we also want them to fit it properly. It's not hard to fit one at all. This video illustrates helmet fitting in a simple way. Check it out. https://www.safekids.org/video/safety-seconds-bike-helmets
The most common helmet fitting mistake I've seen is wearing the helmet too far back on your head. You want it low on your forehead - no more than 2 finger-widths above your eyebrow. Another common fitting issue is wearing it really loose so it moves around on your head. You want to be able to yawn and feel it tug on the top of your head. Finally, I've also seen a lot of unbuckled helmets or even worse - helmets dangling from handlebars. If you don't buckle it wear it at all, it won't be able to protect you when you need it.