@Bristolnewcomer Reflectors are mandatory in winter in a couple of Nordic and Baltic countries. That is probably the reason why there are more articles on them from these countries; and they publish them in English, too.
If I remember correctly, the school children receive these for free, and they are probably handed out during a couple of awareness-raising days, too.
For both adults and children, instead of a new jacket, many seem to wear a hi-viz "rhombus"-format of gear, which you just drop over your clothes and have a reflective "V" at the front and back, like this < >.
If there is a reflector without a clip, unlike the ones from firefly, I often reassemble them with old keyrings or hooks, so that they can be changed quickly between different bags or coats or between different people.
In any case, whatever you will invest in now you can use for many years to come, from pram to kids bike (or your own bike) or cart, and on many different clothes or (school)bags, as pp pointed out, too.