A pediatrician is a doctor who specializes in the regular care of children, as well as the diagnosis and treatment of illness in children. Young patients are often more complicated to treat because they are still growing and developing.
While pediatricians may sub-specialize in specific therapy areas like oncology, surgery, ophthalmology, and anesthesiology, in general, pediatricians provide services like vaccinations, health exams, and treatment of common ailments and injuries. In addition, pediatricians are trained to handle the complex emotional and behavioral issues faced by children, especially during puberty.
Pediatricians normally see their patients from birth until the age of 18, although some may agree to treat patients into their early 20s, if requested.

An allergy & immunology specialist is a physician who is specially trained in matters pertaining to chronic and acute allergies, as well as deficiencies of the immune system. The doctor will determine whether an allergy, which attacks our immune system, is present. They'll also determine the cause, whether it be environmental triggers like trees and pollen, food-borne like peanuts and dairy, the venom of insects like bees, or a medication like penicillin.
In addition to determining the allergen causing an immunological response in a patient, the specialist will treat the symptoms caused by the reaction.

An internist is a physician who focuses on the diagnosis and treatment of conditions that affect the adult population—both acute and chronic.
These doctors are often who adults see as their primary physicians because they treat a broad range of illnesses that do not require surgical or specialist interventions. They also work to help a patient maintain optimal health in order to prevent the onset of disease.
In addition to treating the common cold and flu, internists also treat chronic diseases like diabetes and heart disease.