I started applying for jobs when I was 13. I was turned down by McDonalds (who probably guessed I wasn’t 14 1/2 which was the legal minimum age at that time) and got a much inferior job instead.
Start no earlier than age 14, an age where they start thinking for themselves. 12-16 hours/week. Weekends would be best when parents won’t have to parent and the kids don’t have to think about school for the next day.
They could start their own IRA’s. Employers need the American labor.
Council them against the siren call of cars/stereos.