1. HIV attacks T-cells in the immune system, leading to AIDS in advanced stages.
2. Clinical manifestations in children vary widely and can include failure to thrive, respiratory issues, gastrointestinal diseases, and neurological problems.
3. Diagnosis is made through HIV antibody testing after 18 months or virological testing before 18 months, and management includes prophylaxis, antiretroviral therapy, treating opportunistic infections, adequate nutrition, and immunization.