My son recently had a lot of unexplained black and blues on diff. Parts of his body. Blood test results indicated relative eosinophilia. What's this?

Possible allergies . Due to the bruising a CBC was likely done to exclude a low platelet count (platelets are sticky cells that are an important part of clotting) . A CBC will also give information about anemia and types of white blood cells. One type of white blood cell is an eosinophil, which can be elevated in children with allergies. It may be worth talking to your doctor about furthur testing for allergies.
Insufficent informat. Assuming that the black and blue spots are not due to trauma, it would appear that the boy has abnormal bleeding into tissues. This needs to be evaluated with history, physical examination and additional blood tests. Please consult your doctor for the work-up.