Kiddo worked as an umpire when he was 13-14 I think? He worked (still does) as a junior swim coach at 15. For that job he had to actually do the W-4, etc. There is a work permit required now, and he is 17.
He has also baby-sat and tutored, one-off gigs he gets basically word of mouth, through the swim team. One thing kids do here is sign up to be substitutes for swim meet jobs.
I would second looking at the summer rec organizations. Wherever parents congregate, waiting to pick up kids. Those fliers with tear off tags still work, esp for dog sitting, and “mother’s helpers” type gigs. Same with Nextdoor, but as a parent, I would want to vet whoever is asking my kid to work for them.