Learn Hardcore Norwegian: Barna synes krigshistorien er skummel. - The children think the war story is scary.

barna is by far the most common and is what you should use.
barnene is more old‑fashioned / rare and can sound dialectal or very formal/literary.

So in everyday Norwegian, say barna.

What’s the difference between synes, tror, and tenker, since they all look like “think”?

They all relate to “thinking,” but are used differently:

synes – “to think” in the sense of having an opinion or subjective feeling.
- Barna synes krigshistorien er skummel.
  → The children think/find the war story scary. (their subjective impression)
tror – “to think/believe” about facts, reality, the future, or things you’re not sure about.
- Jeg tror han kommer i morgen.
  → I think (I believe) he’s coming tomorrow.
tenker – “to think” as a mental activity, to be thinking about something, or to plan.
- Jeg tenker på deg. → I’m thinking of you.
- Jeg tenker å reise snart. → I’m planning to travel soon.

In this sentence we are talking about the children’s opinion/feeling about the story, so synes is the correct verb.

Could you also say “Barna synes at krigshistorien er skummel”? Is at required or optional?

Yes, you can also say:

Barna synes at krigshistorien er skummel.

Here, at is a conjunction meaning that, and it introduces the clause krigshistorien er skummel.

In modern spoken and written Norwegian, at is often omitted after verbs like synes, tror, mener, sier, vet, etc., especially when the clause is short and clear:

Barna synes krigshistorien er skummel. (perfectly normal)
Barna synes at krigshistorien er skummel. (also correct, a bit more explicit/formal)

Both are grammatical; leaving at out is very common.

Why is krigshistorien written as one long word instead of krigs historie?

Norwegian usually writes compound nouns as a single word:

krig – war
historie – story, history
krigshistorie – war story / war history
krigshistorien – the war story (definite form)

So instead of writing krig historie as two words, Norwegian joins them:

first part: krig- (war)
second part: historie (story)
plus definite ending: -n → historien → krigshistorien

Writing it as krigshistorien clearly shows it’s one thing: “the war story”, not “war” and “story” separately.

What does the -en at the end of krigshistorien mean?

Historie is a common‑gender noun (like en historie = a story).

(en) historie – a story
historien – the story

When you make the compound:

(en) krigshistorie – a war story
krigshistorien – the war story

So -en here is the definite singular ending for a common‑gender noun: the war story.

Why is it skummel and not skummelt?

Skummel is an adjective meaning scary, spooky.

In Norwegian, adjectives agree with the noun they describe in gender/number:

Common gender (en‑words), singular: skummel
Neuter (et‑words), singular: skummelt
Plural (all genders): skumle

The noun here is krigshistorien = the war story, which is common gender (like en historie).
So we use the common‑gender form:

krigshistorien er skummel – the war story is scary

If the noun were neuter, e.g. et hus (a house), you’d say:

Huset er skummelt. – The house is scary.

What gender is krigshistorie, and what are its basic forms?

The base noun is (en) historie – a story (common gender).
The compound behaves the same way:

(en) krigshistorie – a war story
krigshistorien – the war story
(flere) krigshistorier – (several) war stories
krigshistoriene – the war stories

So you should treat krigshistorie as a common‑gender (en‑word) noun.

How does the word order work in “Barna synes krigshistorien er skummel”?

Break it into parts:

Barna – the children (subject of the main clause)
synes – think/find (finite verb of the main clause)
krigshistorien er skummel – embedded clause = “(that) the war story is scary”

Inside the embedded clause:

krigshistorien – subject
er – verb
skummel – predicate adjective

Norwegian keeps a fairly natural S‑V order here:

krigshistorien er skummel – the war story is scary

After verbs like synes, Norwegian often allows or prefers this “main‑clause‑like” order even when at is omitted, so the sentence is perfectly normal as it stands.

Could you say “Barna synes krigshistorien skummel” without er?

No, that would be ungrammatical in standard Norwegian.

You normally need a linking verb (er = is / are) between the noun and the adjective:

krigshistorien er skummel – the war story is scary

Leaving out er in this structure is not allowed in Norwegian, unlike in some very informal English sentences (“I find this scary” vs. “I find this scary” — where you don’t say “I find this is scary”). Norwegian keeps the er:

Barna synes krigshistorien er skummel.

Is there any difference in meaning between “synes krigshistorien er skummel” and using a construction with det er skummelt?

You could rephrase the idea in different ways:

Barna synes krigshistorien er skummel.
→ Focus: their opinion about that specific story.
Barna synes det er skummelt med krigshistorier.
→ The children think it is scary with war stories / War stories are scary (in general).
Focus: war stories in general, or the situation of having war stories.

So det er skummelt constructions are natural Norwegian, but they usually shift the focus a bit from one specific story to a more general or impersonal statement.

How do you pronounce barna synes krigshistorien er skummel?

Approximate a common Eastern Norwegian pronunciation (IPA in slashes):

barna – /ˈbɑːɳɑ/
- r
  - n often merge into a retroflex ɳ sound.
synes – /ˈsʏːnəs/
- y is like a rounded version of English ee (/yː/).
- Final -es is a schwa sound: /əs/.
krigs‑ – /kriːg/ (in the compound often realized close to /kriːg/)
historien – /hɪˈstuːriən/ or /hɪˈstoːriən/ (dialectal variation)
krigshistorien – often flows as /ˈkriːg(h)ɪstoːriən/ with the g and h blending.
er – /ær/ or /eːr/ (short in everyday speech, /ær/).
skummel – /ˈskʊmːəl/

Said smoothly: [ˈbɑːɳɑ ˈsʏːnəs ˈkriːg(h)ɪˌstoːriən ær ˈskʊmːəl]
Stress mainly on BÁR‑na, SÝ‑nes, KRIG‑his‑TOR‑ien, SKUM‑mel.

What is the past tense of synes, and how would the sentence look in the past?

The past tense of synes is syntes.

synes – think (opinion, present)
syntes – thought (opinion, past)

So in the past tense, you’d say:

Barna syntes krigshistorien var skummel.
→ The children thought the war story was scary.

Note that er (is) also changes to var (was) to match the past.