Barnið borðar morgunkorn og drekkur mjólk áður en það fer í skóla.

Barnið means the child. Icelandic usually adds the definite article to the end of the noun, instead of using a separate word like English the.

• barn = child
• barnið = the child

The ending -ið is the definite article for this neuter noun.

Because barn is a neuter noun in Icelandic, the pronoun used for it is also neuter:

• barn = a neuter noun
• það = it

So even though English often says he or she for a child, Icelandic can naturally use það when referring back to barnið.

These are all present tense, 3rd person singular verb forms:

• borðar = eats
• drekkur = drinks
• fer = goes

They match the subject barnið because the child is singular.

In Icelandic, the simple present tense often covers meanings that English expresses with either:

• eats / drinks / goes
• is eating / is drinking / is going

So Barnið borðar morgunkorn can mean The child eats cereal or, depending on context, The child is eating cereal.

In this sentence, it most naturally sounds like a habitual action: the child eats cereal and drinks milk before going to school.

Because the subject is the same in both parts of the sentence:

• Barnið borðar morgunkorn
• og drekkur mjólk

This means The child eats cereal and drinks milk.

Just like in English, Icelandic does not need to repeat the subject when two verbs share the same subject.

Morgunkorn means breakfast cereal or simply cereal.

It is a compound noun:

• morgun = morning
• korn = grain

So the literal idea is something like morning grain, which Icelandic uses for cereal.

Yes, Icelandic does use cases, and the direct object after these verbs is normally in the accusative.

In this sentence:

• morgunkorn is the object of borðar
• mjólk is the object of drekkur

However, not every noun changes visibly in every case. Mjólk happens to look the same here, even though grammatically it is functioning as an object.

So the important point is: the sentence does use case, but the noun form does not always visibly change.

Áður en means before when it introduces a clause.

So:

• áður en það fer í skóla = before it goes to school

A useful way to remember it is that áður is related to earlier / before, and en here links the following clause.

Fara í skóla is the normal Icelandic expression for go to school.

The preposition í often means into / in / to, depending on context. With movement, it can mean going into a place or institution.

So:

• fara í skóla = go to school
• vera í skóla = be in school / be at school

This is a standard Icelandic way to express attendance at school, not just physical movement toward a building.

Because í skóla often means to school in a general, institutional sense, much like English says go to school rather than always go to the school.

Compare the difference:

• fara í skóla = go to school in general
• fara í skólann = go to the school / go into the school building

So in your sentence, í skóla is the natural idiomatic choice.

The clause follows normal subject-verb order:

• það = subject
• fer = verb
• í skóla = prepositional phrase

So literally it is:

• before it goes to school

Nothing unusual is happening there; it is a straightforward subordinate clause introduced by áður en.

These two letters are very important in Icelandic:

• þ is like the th in thin
• ð is like the th in this

So:

• það begins with the th sound of this, even though it is spelled with þ
• borðar and áður contain ð, which is usually a voiced th sound

Very roughly:

• það ≈ thath
• áður ≈ OW-thur
• borðar ≈ BOR-thar

These are only approximations, but they help beginners.

Most likely it describes a habit or a typical routine:

The child eats cereal and drinks milk before going to school.

Because Icelandic present tense can cover both habitual and current actions, context decides the meaning. Without extra context, this sounds like a general routine rather than a one-time event.