There are a few things to cover here. First, his initial WBC count is quite high; however, since it dropped back down on the next test, the initial elevated white count was likely due to something called a leukemoid reaction. Basically this is where the body responds to an infection so dramatically that it increases the WBC count into the range commonly seen with leukemia (hence the name leukemoid). This is NOT due to a cancer and is really a harmless thing.
Now, regarding the microcytosis and anisocytosis. Microcytosis means small red blod cells. This correlates with an MCV (mean cell value) of 69 (low). Anisocytosis means the red blood cells are of varying sizes. This corresponds to the RDW (red cell distribution width) that is elevated.
The most common cause of an elevated RDW and a low MCV is, by far, iron deficiency. I would suggest you talk with your son's pediatrician about some iron supplementation to help rebuild his stores. After 2-3 months of iron supplementation, I suspect the MCV will be normal and the RDW will have decreased back to normal as well.
There are a few other possible causes but iron deficiency is much, much more common so trying to correct this is the first step. If there is doubt as to whether or not this is from iron, iron levels can be measured. This is done by testing basically three things-iron level, ferritin level, and total iron binding capacity (or sometimes transferrin saturation instead of the TIBC). Iron deficiency has low iron levels, generally low ferritin levels (although this can be affected by other things), and a high TIBC or low transferrin saturation.
Advice and opinions given are based on the information provided and must not be considered an official medical recommendation. The limitations of the internet prevent an appropriate evaluation. Always consult your doctor if there is concern.