Hello,
Thank you for your question and pictures.  Your little trees appear to be suffering from leaf scorch.  I notice the brown lawn in the background of the pictures, indicating that it has been dry where you live.  The same has been true in my area of Clark County.
The treatment is proper and more frequent watering, adjusting according to the weather.  The link below will give you some guidelines.
https://extension.umn.edu/planting-and-growing-guides/watering-newly-planted-trees-and-shrubs

In addition, buckeye trees have a tendency to get leave blotch.    This quote is from Ohio Dept. of Natural Resources:
“Unfortunately, leaves of Ohio buckeye become very prone to scorching, discoloration, and foliar diseases by mid-summer...”

Here is the rest of the article:
https://ohiodnr.gov/discover-and-learn/plants-trees/broad-leaf-trees/ohio-buckeye-aesculus-glabra#:~:text=Ohio%20buckeye%20often%20suffers%20from,in%20mid%2D%20to%20late%20summer.

From Buckeye Yard and Garden Line (BYGL), more about leaf diseases on buckeyes
https://bygl.osu.edu/node/837

I hope this information is helpful to you.  Again, thank you for using the Ask Extension online service.

Hi

Scott,
You are more than welcome!  So glad you found the info helpful!