- migrant children show up and work and just lie about their age or supply forged documentation, which is impossible to verify for the company or any US agency.
- not enough government inspectors, and not enough latitude during inspections for private inspectors; e.g., having to request permission to show up on second shift.
(2) is easy to solve with money, but I have no idea what anyone could be expected to do about (1), unless you decide to aggressively prosecute companies relying on migrant workers, which is politically untenable for both parties.