Irish Kilt?

[Laighneach]

Here is the still from The Quiet Man with John Wayne's sons wearing kilts:

The clothing worn by the two boys in this picture isn't as far off the mark as some may assume.
Young boys traditionally wore a skirt-like garment, called a "cóta cabhlach" if I recall correctly. This custom lasted longest in places like the Aran Islands.
Caps of the type shown were very common too (still made I think).