Looking up...
Mi nieto es muy travieso.
My grandson is very mischievous.
The son of one's child; a male grandchild.
Ella adora a su nieto.
She adores her grandson.
The feminine form is 'nieta' (granddaughter).
Remember that 'nieto' is masculine, while 'nieta' is feminine.
From Latin 'neptus', meaning 'grandson'.
In Spanish, 'nieto' specifically refers to a male grandchild. For female grandchildren, use 'nieta'.