Learn Hardcore Norwegian: Barn leker på fortauet ved krysset, så bilene må stoppe. - Children play on the sidewalk by the intersection, so the cars must stop.

Barn leker ... = Children are playing ... (general statement)
Noen barn leker ... = Some children are playing ... (an unspecified group, but not “all children”)
Barna leker ... = The children are playing ... (a specific group that speaker and listener know about)

Here, Barn leker på fortauet ved krysset is a general, scene‑setting statement about children (not a particular, previously mentioned group), so the bare plural barn is natural and common.

Is barn singular or plural here? How can I tell, since the word looks the same?

Barn is a special noun: it has the same form in singular and plural.

Indefinite singular: et barn – a child
Definite singular: barnet – the child
Indefinite plural: barn – children
Definite plural: barna – the children

In this sentence, you know it is plural from the verb form and context:

Barn leker ... → the verb leker normally matches a plural subject in meaning here (children play / are playing).

If it were singular definite, you would expect Barnet leker ... (The child is playing ...).

Why is Barn capitalized? Does Norwegian capitalize all nouns like German?

No. Norwegian capitalizes nouns only when they are:

At the beginning of a sentence
Proper names (people, places, brands, etc.)

Here, Barn is capitalized just because it’s the first word in the sentence. If it were in the middle of a sentence, it would be written barn. Norwegian does not capitalize all nouns as German does.

What is the difference between leker and spiller? Why is it leker here?

Norwegian usually distinguishes between two verbs that in English both translate as play:

å leke – to play in a childlike, free, non‑structured way (running around, playing with toys, pretending, etc.)
å spille – to play a game or sport with rules, or to play an instrument (chess, football, guitar, etc.)

Since children on a sidewalk are likely playing in an informal, childlike way, leker is the natural choice:

Barn leker på fortauet ... = Children are playing on the sidewalk ... (in a general, childlike way)

Why is it på fortauet and not i fortauet or something else?

The preposition på is used for surfaces and many “on” locations:

på bordet – on the table
på gulvet – on the floor
på fortauet – on the sidewalk / pavement

The sidewalk is understood as a surface you are standing or moving on, so på is the normal preposition.

I fortauet (in the sidewalk) would sound strange, as if you were somehow inside the material.

Why is it fortauet (definite form) instead of just fortau?

Fortauet is the definite singular form:

et fortau – a sidewalk
fortauet – the sidewalk

Norwegian tends to use the definite form when both speaker and listener can identify which thing is meant. In a typical street scene, there is a specific sidewalk by that intersection, so:

på fortauet ved krysset = on the (particular) sidewalk by the intersection

Using på et fortau ved et kryss would sound more like describing some random, unspecified sidewalk and intersection, which is less natural here.

What exactly does ved krysset mean, and how is ved different from nær?

Ved here means by / next to / at, in the sense of “right by the side of”:

ved krysset – by the intersection, at the intersection

Compared with:

nær krysset – near the intersection (in the vicinity, but not necessarily right at it)

So på fortauet ved krysset suggests the children are on the part of the sidewalk that is right by that specific intersection.

Why is krysset also in the definite form?

Kryss (intersection, crossing) behaves like this:

et kryss – an intersection
krysset – the intersection

Again, the definite form is used because we are talking about a specific, identifiable intersection (in this imagined scene). Norwegian often uses definite forms for things that are contextually clear, like:

på skolen – at school
i hagen – in the garden
ved krysset – at the (known) intersection

Why is it bilene and not just biler?

Bilene is definite plural:

en bil – a car
biler – cars
bilene – the cars

We’re talking about the cars that come to this intersection and see these children. In context, they’re a specific, identifiable group, so Norwegian naturally uses the definite plural:

... så bilene må stoppe.
... so the cars have to stop.

If you said så biler må stoppe, it sounds more like so cars must stop as a general rule, not about the particular cars there.

Why is it må stoppe and not må å stoppe?

In Norwegian, modal verbs are followed by a bare infinitive (infinitive without å):

Common modals:

kan – can
må – must / have to
skal – shall / going to
vil – want to / will
bør – should

Pattern:

Subj + modal + bare infinitive

So you say:

Bilene må stoppe. – The cars must stop.
not
Bilene må å stoppe. ✗

The å is dropped after these modal verbs.

Why is there a comma before så? In English, I might or might not put a comma before so.

In Norwegian, there is a strong tendency (and in standard written language, a rule) to put a comma between two main clauses that are joined by a conjunction like og, men, eller, for, så.

Here you have two main clauses:

Barn leker på fortauet ved krysset
bilene må stoppe

They are joined with så, so you write:

Barn leker på fortauet ved krysset, så bilene må stoppe.

Leaving out the comma would usually be considered incorrect in standard written Norwegian.

Does så here mean “so” (result) or “then”? Does it change the word order?

Here, så is a coordinating conjunction meaning so / therefore, introducing a result:

(...), så bilene må stoppe. – ..., so the cars have to stop.

With så as a conjunction in the middle of a sentence, the word order in the next clause is normal: subject before verb:

så bilene må stoppe (subject bilene before verb må)

Compare with så used as an adverb meaning then at the beginning of a sentence:

Så må bilene stoppe. – Then the cars have to stop.
Here så comes first, and Norwegian uses verb‑second word order: må (verb) comes before bilene (subject).

So:

Conjunction så in the middle: ..., så bilene må stoppe.
Adverb så at the beginning: Så må bilene stoppe.

Could I say Derfor må bilene stoppe instead of så bilene må stoppe? Is there any difference?

You can say:

Barn leker på fortauet ved krysset, derfor må bilene stoppe.

This is grammatical, but the nuance is slightly different:

så is more neutral and conversational as a connector meaning so, very common in everyday speech and writing.
derfor literally means therefore, and sounds a bit more formal / explicit about the cause‑and‑effect.

Both express a result, but så is usually the most natural and colloquial in a sentence like this.