I find this interesting...
my gr gr grandfather was Patrick Haley born 1796 Ireland.
He was married to a Mary born 1810 Ireland.
in the 1860 census of New York it shows 2 children:
Bridget 8 yrs.
Patrick 4 years
They also had living with them a Mary Haley that I assume is
Patrick "Sr." sister born 1806 Ireland. Patrick, mary and mary disappear after that. Only the kids show up in 1880 census.
Let me know if this is useful.