The goal of this clinical study is to learn more about the safety and dosing of study drugs, cobicistat-boosted Atazanavir (ATV/co), cobicistat-boosted darunavir (DRV/co) and emtricitabine/tenofovir alafenamide (F/TAF), in children (age ≥ 4 weeks to \< 18 years) with HIV.