EU road safety commission policy and the programme of pushing helmet wearing is massive and has a very influential bearing on helmet wearing rates, catching them whilst they are young so they are either put off cycling or forced/indoctrinated into the noddy hat world of cycling.
This second image is the opening page on the EU road safety site, the first screen grab is atypical of the way that countries are being led to push children to wear helmets and hi-vis. Even the Danes and Dutch have had significant rises in helmet wearing, and what happened in NL, death and injury rates went up

Note the lies re hi-vis and the stats being used are deliberately misleading, incomplete and when compared to motoring and walking head injuries are minuscule. According to the EU road safety commission, UK is safer than NL and DK for cycling because we wear more helmets, they even made a massive point about the then circa 185 deaths in NL being more than that in the Uk and then basically made out it was due to helmet wearing rates in their report of 2016

