Holes in the foliage does not sound like aphid. Instead you may have caterpillars that hide on the back of the foliage and match the color of the leaves. The trees look small enough that you can remove the most damaged leaves and any caterpillars you find. Spray the underside and top of the leaves with Bt (Bacillus thuringiensis) if the problem persists and if the tree loses more than a third of it's leaves due to the pests reach for stronger pesticides container pyrethrum or rotenone. There is another possibility that your cherry trees have a fungal infection called shot hole disease. If you do not find any caterpillars, worms or other insects then suspect this leaf disease instead. Keep growing, Marianne Binetti