According to the 2014 Supplier Responsibility Report issued by Apple yesterday, Apple's suppliers do not use unethically sourced tantalum. The report is based on the audit done by third-party auditors.
This means that the materials used to build your favorite device have not been gathered in war-torn regions of Africa. The report also highlights a number of other achievements for 2013 such as driving suppliers to achieve a 95% compliance rate with the company's standard maximum 60-hour workweek.
Apple also take maximum care to avoid exploiting underage work force. When the company revealed one of its Chinese suppliers to be systematically engaging in such a practice, Apple dropped the supplier.