UK government (and the rest of Europe) has had a very easy time implementing strict administrative regulations due to public acceptance. And the children argument is like the easiest angle to attack, you can use it for almost any cause and win.
Similar to a lot of other Japanese phrases out there - "ikigai", etc. It's quite uninteresting as someone who's Japanese or lived in Japan, but an extra level of meaning is attached when projected outwards
The definition of 'work' itself is pretty arbitrary. Someone writing for fun could end up being 'work' if it inspires some large change in the world. And someone doing lots of labor could barely move the needle.
In that sense, not everyone (who is eligible to work or looks like they are working) is working in the first place.