The English language has no collective term that would cover both nieces and nephews, other than the general word "relatives."
According to Merriam Webster & Wikipedia; 'niblings' (play on siblings) is a collective term for nephews and nieces.
Your niece and nephew are the daughter and son, respectively, of your sister or brother. When talking about them, you may call them "my niece" or "my nephew" or something similar. When talking t them, you wold generally call them by name.
grand/niece/nephew
Relatives
Nieces and nephews are the children of your siblings.
Nephews and/or Nieces
They are your nieces and nephews and not your cousins
Nieces are the daughters of your brothers and sisters. Nephews are the sons of your brothers and sisters.
Mark Twain's nieces and nephews were the children of his siblings, which included nieces Ida, Susy, and Clara, and nephews Samuel, Frank, and Willie.
They are your grand-nephews and grand-nieces or great-nephews and great-nieces.
Yes, he did have nieces and nephews. Three of his brothers and three of his sisters lived to maturity and together gave him more than 30 nieces and nephews.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
Jane Austen never married and had no children.
Nephews: Landon, Caleb, Nieces: Rylie, Sydney, Josie, Reagan
Rachel Carson did not have any biological children, so she did not have any nieces or nephews.
She has two nieces