The caterpillars are those of the Orange-striped Oakworm Moth, a native and common species that, as the name implies, eat oak as their host plant. Although they can defoliate individual branches, they don't cause serious damage to the tree and it will recover just fine on its own. (It's normal if the denuded branches don't produce much in the way of new leaves, if any, this late into the growing season. They will still develop leaf buds for next year's growth that will lie dormant on the branches until spring.) No intervention is necessary, and birds and other animals may snack on some of the caterpillars in the meantime.

The egg-like growth on the oak leaf is not actually an egg but a type of gall. Plant galls are somewhat akin to a tumor, though benign in this case. Oaks can develop a wide range of gall types, and those on foliage will disappear as the leaves fall this autumn. No intervention is needed for this either.

Miri