Answer:
Both a psychologist and a psychiatrist can hold therapy sessions with the child in question.
A psychiatrist is a medical doctor that has received specialized training after the standard medical school stint, whereas a psychologist is not. Psychiatrists are also the only one out of the two who can write prescriptions for medication.
Usually, a psychologist will work with the child first, and if he or she determines that there is a need for medicine, he or she will then refer the child to the psychiatrist.