It's pretty well-known that the point of an internship isn't to actually accomplish any useful work, it's to determine which students you would like to extend an offer to for full-time employment. Not a large leap to assume that a lot of adolescent employment follows this pattern. The wages you'd pay a teen are chump change for most businesses, but responsible, intelligent, trustworthy employees basically disappear from the job market after their first job (because everybody wants to keep them), and so it can be a great investment to identify, vet, and introduce yourself to them before they're on the open market.