I read my first Saki (H.H. Munro) short story when I was a pre-teen, and I still remember it. It was The Open Window, and is included in Beasts and Super-Beasts, available at Project Gutenberg.
http://www.gutenberg.org/ebooks/269
It's also available here in the MobileReads Library:
https://www.mobileread.com/forums/sho...d.php?t=198451
Munro died in 1916, so everything should be in the public domain.
The Open Window is a bit spooky, but also very funny -- perfect for a kid, IMHO, but you know your child best.