If sub-optimal adherence is the reason why children are failing 2nd line treatment, then restoring optimal adherence should result in viral suppression, failure of which might mean that other causes are contributing to failure. If resistance is the cause of treatment failure, then this study will provide evidence for advocating for resistance testing and the use of 3rd line antiretroviral drugs. If children with adequate adherence demonstrate inadequate drug levels in their plasma, then this study will provide evidence to advocate for studies to examine reasons for inadequate drug exposure amongst HIV-infected children. These studies are paramount to optimizing dosing algorithms in this population.