Garden Pests and Diseases: What's eating my redbud leaves?, 1 by Quadrivium

Quadrivium wrote:
I have several small redbud saplings (eastern redbud, I assume), only a few years old. Until this year they looked perfectly healthy. But now something is eating holes in the leaves, apparently making very clean, nearly circular cuts. Some leaves are more than half gone. The remaining portions of the leaves look healthy. I don't see any insects on the trees, or any other clues. Curiously, I also have a couple of full-grown redbuds, and their leaves are almost completely unaffected; whatever it is, it seems only to be attracted to the small saplings. Any ideas what this is?