Do child stars start with many acting classes, acting in community theater, commercials, and student films?

I never saw any of these child stars in commercials before they became famous. Do they have to put in the same effort learning audition skills, marketing themselves, getting head shots (with parents' help), and putting in the same effort as adult actors? That is do the children treat it as a job the way adult actors do? Do child actors auditioning for PBS shows have to meet the same standards as children auditioning for network TV? I read that 2,000 to 3,000 actors audition for each role on each role on a TV show. This this also apply to child actors auditioning for PBS shows?