4 yr/old has slightly elevated mcv and mch. all other blood values are in perfect range. dr. doesnt seem concerned. benign or needs further testing?

Look at the smear: If the elevation of the MCV is slight, and the peripheral smear is normal, and junior feels well, the wisdom is "don't treat a lab value." consider checking it in a few months. Hemolysis insufficient to cause anemia, hypothyroidism, early megaloblastic anemia, & artifact from 2 rbc's being counted as 1 are all considerations should the high MCV persist.