A recent study from the Ethical Trading Initiative (ETI) shows that a) child labour is still one of the biggest issues in the supply chain, b) "zero tolerance" approach is not enough and c) often child labour gets "redistributed" to the less regulated areas further up the supply chain.
The report can be found at here, it definitely is a worthy read and I would also recommend to pick up some ideas on what to do more than just audit. Although "all" is common sense it definitely makes sense to reassess how one´s business practices affect the situation of child labour and what should be done to improve remediative actions.