Learn Hardcore Icelandic: Fjöldi barna leikur sér á litlu svæði fyrir framan húsið. - A number of children play in a small area in front of the house.

The grammatical subject here is fjöldi (fjöldi barna = “a number of children / many children”).
Fjöldi is a singular noun (masculine, nominative singular), so the verb is also singular: leikur.

Literally: Fjöldi barna leikur sér ≈ “A number of children plays.”
Even though in English we’d use a plural verb (“play”), Icelandic keeps it singular.

2. Why is it barna and not börn after fjöldi?

Barna is the genitive plural of barn (“child”).

Nominative plural: börn (“children”).
Genitive plural: barna (“of children”).

The noun fjöldi (“number, crowd”) normally takes a genitive to show what there is a number of:

fjöldi fólks – a number of people
fjöldi bíla – a number of cars
fjöldi barna – a number of children

So barna is required because fjöldi governs the genitive case.

3. What does leikur sér literally mean, and why do we need sér?

Leika sér is an idiomatic verb phrase meaning “to play, to amuse oneself.”

leika on its own can mean “to play (a role, an instrument), to perform”.
When you add the reflexive pronoun sér (dative of sig), it becomes the everyday verb for children playing.

So:

Börnin leika sér. – The children are playing.
Fjöldi barna leikur sér. – A number of children is playing.

Grammatically:

sér is the dative reflexive pronoun referring back to the subject.
Certain Icelandic verbs naturally use sig / sér; leika sér is one of them. You generally can’t drop sér here if you mean “to play” in the children-having-fun sense.

4. Why is it á litlu svæði and not something like á lítið svæði?

The preposition á (“on, at, in”) can take either dative or accusative, depending on meaning:

Dative = static location (where something is)
Accusative = movement towards / onto (where something goes)

In this sentence we are talking about where the children are playing (a location), not where they move to. So á takes the dative:

svæði is neuter; its dative singular form is also svæði.
The adjective lítill (“small”) in dative neuter singular is litlu.

So:
á litlu svæði = “on / in a small area” (location, hence dative).

If you were describing motion onto the area, you could use accusative:
Hann fór á lítið svæði. – He went onto a small area.

5. Why does the adjective appear as litlu? What form is that?

The base adjective is lítill (“small”). Its relevant forms (strong declension) are:

Nominative neuter singular: lítið
Accusative neuter singular: lítið
Dative neuter singular: litlu
Genitive neuter singular: lítils

Because á here takes the dative (location), we need the dative neuter singular form:

litlu svæði = “small area” in the dative case.

It looks “odd” mostly because learners get used to seeing lítið with neuter nouns first; litlu just shows it’s in the dative.

6. Why is svæði in the dative if it looks unchanged?

Many neuter nouns in Icelandic have the same form for several cases. Svæði is one of them.

Singular of svæði (n.):

Nominative: svæði
Accusative: svæði
Dative: svæði
Genitive: svæðis

So even though the form svæði doesn’t change, the phrase á litlu svæði is in the dative because:

The preposition á indicates location here (so it must be dative), and
The adjective litlu clearly shows dative neuter singular.

The case is determined by the grammar, not by a visible ending on svæði in this instance.

7. What exactly does fyrir framan mean, and is it one unit or two separate words?

Fyrir framan functions as a compound prepositional phrase meaning “in front of.”

fyrir alone can mean “for, before, in front of, because of” (and can take different cases).
framan on its own is related to “front, forward”.

When combined as fyrir framan, they behave like a single preposition:

Meaning: “in front of” (spatially)
Case: it normally takes the accusative.

Example:

fyrir framan húsið – in front of the house
fyrir framan bílinn – in front of the car

8. Why is it húsið and what case is it in?

The base noun is hús (neuter: “house”).

Its singular forms (indefinite):

Nominative: hús
Accusative: hús
Dative: húsinu
Genitive: húss

Definite singular (with the article suffix):

Nominative: húsið
Accusative: húsið
Dative: húsinu
Genitive: hússins

In fyrir framan húsið:

fyrir framan takes the accusative.
húsið is therefore in the accusative singular definite, but for this noun, nominative and accusative definite have the same form (húsið).

Semantically: húsið = “the house” (not just “a house”).

9. Why is there no separate word for “the” before húsið or “a” before fjöldi?

Icelandic handles articles differently from English:

Definite article (“the”)
- Usually attached as a suffix to the noun (or to the adjective+noun phrase), rather than as a separate word.
- hús → húsið = “the house”.
  So húsið already contains “the”.
No indefinite article (“a / an”)
- Icelandic has no separate word for “a/an”.
- fjöldi barna can mean “a number of children” or just “number of children,” depending on context.

So:

fjöldi barna – “(a) number of children / many children”
húsið – “the house”

10. Could I say Mörg börn leika sér á litlu svæði fyrir framan húsið instead? What’s the difference from Fjöldi barna…?

Yes, you can say:

Mörg börn leika sér á litlu svæði fyrir framan húsið.
– “Many children are playing in a small area in front of the house.”

Differences:

Fjöldi barna literally focuses on “a number / crowd of children”. Grammatically singular, slightly more formal or descriptive; it treats the group as a unit.
Mörg börn simply means “many children” as a straightforward plural subject.

Both are natural, but:

Fjöldi barna leikur sér… subtly emphasizes the size/amount as a collective group.
Mörg börn leika sér… is a more direct plural “many children play…”

11. Can the word order of the prepositional phrases change? For example, could I say …fyrir framan húsið á litlu svæði?

You have some flexibility in word order, but not every variant sounds equally natural.

Original:

Fjöldi barna leikur sér á litlu svæði fyrir framan húsið.

Possible and understandable alternatives:

Fjöldi barna leikur sér fyrir framan húsið á litlu svæði.
– Still understandable, but the information structure shifts slightly; it may sound a bit heavier or less smooth to some speakers.

Generally:

Icelandic usually puts location phrases after the verb, often from more general to more specific or in the order that feels most natural.
Here, á litlu svæði and fyrir framan húsið both describe location. The original order sounds very normal.

You normally wouldn’t separate them with other material, but swapping their order is grammatically okay; it just affects emphasis and flow.

12. What’s the difference between leikur sér and er að leika sér? Could we use er að leika sér here?

Yes, you could say:

Fjöldi barna er að leika sér á litlu svæði fyrir framan húsið.

Difference in nuance:

leikur sér – simple present; in Icelandic this can cover both habitual and right-now actions.
er að leika sér – a periphrastic progressive, often focusing more clearly on an action happening right now (similar to English “is playing”).

In everyday speech, both are used; leikur sér is a bit more neutral/compact, er að leika sér can make the ongoing nature especially explicit. Both are grammatically fine in this sentence.

13. How is fjöldi pronounced, and how do I pronounce the vowel ö?

Fjöldi is pronounced roughly like:

[ˈfjœl̥.tɪ]
- fj: like f + a palatal-ish j-glide, somewhat like “fy” in “few”, but with a clearer [j].
- ö: a front rounded vowel [œ], somewhat between English “e” in “bed” and French “eu” in peur.
- ld: the l may be voiceless here; Icelandic often devoiced before certain consonants.
- i at the end: like short “i” in “bit”.

You can approximate ö by:

Saying the English “e” of “bed”,
Then rounding your lips as if for “o”, but keeping the tongue where it was for “e”.