I'm NOT condoning the behavior. This is disgusting. Still, "the supplier would (within a few hours) stop using child labour" is completely unrealistic.

Apple should have cut ties immediately even if it meant a breach of contract or shortage of inventory.

For some reason I was looking at pictures of textile equipment recently. Some of that equipment is built so that it's only accessible to growing children or adults with growth disorders. That's structural bias to such a degree that it is in fact literal. The requirement of child labor is literally built into the factory. I have no way of knowing if that's true for this factory, but if they're capitalistic at all then accessibility for (local) above-average humans is an opportunity cost that would have been eliminated in the name of efficiency. And if that worked so well why not try it again on the next assembly line, only goosed a little harder?

In any case, there is no "overnight" because you have to train new people for a high throughput task. But would you even believe them once they did?

For the west that's such a basic boundary at this point that if someone goes past it, it's because their ethical model is so different from yours that you can't reason about whether they've actually done what you've asked, or they've employed a new coping mechanism to seem 'normal'. Like just rearranging the factory so that your section has all the people over 16, which means the other building is now almost entirely children (making the situation more dangerous, not less). Or the children work second shift when you won't be around to audit, which is both dangerous and more unhealthy.

They didn't get your objection to begin with. Their response is likely to resemble the sort of thing a sociopath would do: identify your discomfort and arrange for it never to be triggered, rather than truth and reconciliation.

I'm worried if Apple didn't push hard enough during all that 3 years, and later they moved to a different supplier for other reasons.