A pediatrician is a doctor who focuses on the health of infants, children, adolescents and young adults. Pediatric care starts at birth and lasts through a child's 21st birthday or longer. Pediatricians prevent, detect and manage physical, behavioral and developmental issues that affect children. Paediatricians are medical specialists who diagnose, treat, and provide medical care for babies, children and teenagers. They treat illnesses and will check your child's physical, mental and behavioural development.