> There is also evidence that teens who have part-time jobs are happier than those who don’t, because of the sense of independence and confidence they gain from the job.

Genuinely wondering where they got any data for that, given that child labour is generally illegal these days and all. What kind of part time jobs for children that pay actual money exist in the present?

I suppose you've got the rare ones like acting, modelling, toy testing, but those come with a lot of other factors that are probably hard to control for and in most cases I doubt the kids are paid directly. Maybe they counted getting $5 from your parents for mowing the lawn.