pediatrician; paediatrician
A medical doctor specializing in the care of children.
She is studying to become a pediatrician.
My child had a fever, so we saw a pediatrician.
小児科 is the department of pediatrics, while 小児科医 is the doctor who works in that department.
医者 is a general term for a doctor, while 小児科医 specifically refers to a pediatrician.
Compound of 小児 (shōni, 'child') + 科 (ka, 'department') + 医 (i, 'doctor').