For whatever relevance, my old edition of The Norton Anthology of English literature footnotes The Wild Swans at Coole with, "I.e., Coole Park, Lady Gregory's country estate, where Yeats was a frequent guest." The Yeats chapter's introduction states that beginning in 1897, at this Galway estate he "discovered the attractiveness of the 'country home ideal', seeing in an aristocratic life of elegance and leisure in a great house a method of imposing order on chaos and a symbol of the neo-Platonic dance of life."

Another oldie-and-moldie text, The College Survey of English literature, includes the volume entitled "The Wild Swans at Coole" among Yeats' later work, in which he moved away from songs (in the poet's words) -

Covered with embroideries Out of old mythologies.

In 1924 he wrote: "My friends and I loved symbols, popular beliefs, and old scraps of verse that made Ireland romantic to herself; but the new Ireland, overwhelmed by responsibility, begins to long for psychological truth."

Now, whether and/or how this may or may not pertain to the Children of Lir, I dunno.