Answer:
Send CBC and peripheral smear
Explanation:
The symptoms shows that the boy is suffering from leukemia, of which the type known as Acute Lymphocytic Leukemia is more associated with Down Syndrome.
Therefore, it will be best to send CBC and peripheral Smear.
CBC which means Complete Blood Count, evaluate the level or degree of leukemia, anemia, and White Blood Cell (WBC) count.
Also, With the help of Smear to diagnose if the child is suffering from leukemia.