Questions & Answers about Barnið kann að synda vel.
Because barnið is the definite form: the child.
- barn = a child
- barnið = the child
In Icelandic, the definite article is usually attached to the end of the noun instead of being a separate word like English the. Here, -ið is the definite ending used with this neuter singular noun.
No. This is just grammatical gender, not biological sex.
Icelandic nouns belong to grammatical genders: masculine, feminine, or neuter. The noun barn happens to be neuter, so it takes neuter forms like barnið.
That does not tell you whether the child is a boy or a girl. It only tells you how the word behaves grammatically.