This is the 666th most frequent Icelandic word.
barn
Child.
Here, 'barn' is used as a noun meaning 'child', specifically in the definite form 'Barnið'.
Barnið hljóp í garðinum.
The child ran in the garden.
In this instance, the plural form of 'barn', which is 'börn', is used to denote 'children'.
Hún á tvö börn.
She has two children.
The compound form 'Barnabarnið,' which combines 'barn' ('child') and 'barnabarn' ('grandchild'), indicates a grandchild, showing how 'barn' integrates into a compound noun.