what would my sister's son's daughter be to me?
Your sisters son is of course your nephew,You are his Aunt...
Your Nephews daughter would be your great-neice,you would be her great-Aunt.
Your sister's daughter is your niece and you are either her aunt (if you are a woman) or her uncle (if you are a man). The English language uses the same term for the daughter of a younger sister and the daughter of an older sister.
Your sister's daughter is your niece. You are her aunt (if you are female) or her uncle (if you are male).
Your sister's daughter would be your niece.
Your sisters daughter is your niece.
Your sisters daughter is your niece.
A cousin, in all those difficult cases they are your cousins
Your daughter and your nephew are first cousins. His daughter is your daughter's first cousin, once removed.
Nephews
your nephews
Some would call your nephew's children your grand nephews and grand nieces, others would call then your great nephews and great nieces.
your niece's or nephews
If it is a boy then it is your nephew. If it is a girl then it is your niece.
Your daughter is you great nephews great cousin if u live in Australia ,USA ,UK
nephews!
Children of your siblings are nieces and nephews. Children of your spouse's siblings are still called nieces and nephews, but you are not related to them by blood.
Second cousins once removed.
Your nephew's child is your great niece (if a girl) or your great nephew (if a boy).