So, even though the gravestone inscription is confusing, I think the Daisy and Willie mean the children of their son William.
I listed all their children in a previous message, including:
Daisy CHRISTIAN 8 Sep 1888 Fox [father] William CHRISTIAN [mother] Margaret CORLETT.
William Rob CHRISTIAN 23 Jul 1879 Pat, William CHRISTIAN, Margaret Ann CORLETT

It looks as though son William went to the USA on his own, leaving his wife and children behind? Perhaps they were to follow him after he got settled, or after the baby was born - but then he died suddenly.

Sue