Thank you for including such a nice photo with your question!  Those are indeed buckeye lace bugs.  As with all lace bugs, they use their piercing/sucking mouthparts to feed on the contents of plant cells in the leaf.  Their feeding damage produces small yellow spots we call "stippling."  This lace bug feeds on the lower leaf surface, but, if the stippling coalesces, you may see large areas that look faded or even white on the upper leaf surface.

The good news is that I've never seen this lace bug cause serious damage to the overall health of established buckeye trees.  So, your concern should lesson as your tree becomes established and grows.  However, we are always concerned with leaf damage to newly planted trees.  Thankfully, lace bugs are pretty easy to control with many over-the-counter insecticides.

First, make sure to read and follow product label directions closely!  Look to see if the product you select says it controls lace bugs and it does not warn against applying to buckeyes; ideally it would be good if buckeyes and/or horsechestnuts are on the label.  This means it's safe to apply to your tree.  Second, if you use a "contact spray" on the foliage, make sure you're doing a good job covering the underside of the leaves where the  lace bugs live.  Finally, depending on the product, you may need to make more than one application because no insecticide will kill the eggs; you will only kill the nymphs and adults.  Once the eggs hatch, the damage will start all over again.