Learn Hardcore Norwegian: Barnet finner helsekortet sitt.

You mostly have to learn the gender with each new noun. There’s no reliable rule that tells you barn is neuter; it’s just part of the word’s dictionary entry.

When you look up barn in a dictionary, it will usually say something like:

barn (n) or barn (et)

The (n) or (et) tells you it’s neuter. That’s why you get:

et barn (a child)
barnet (the child)

Why is the verb finner used here, and does it change with the subject?

Finne is the infinitive (to find). The present tense is finner for all subjects:

Jeg finner – I find
Du finner – You find
Barnet finner – The child finds
Vi finner – We find

Norwegian doesn’t change the verb for person or number in the present tense, so it’s always finner.

Why is it helsekortet and not helsekort?

Helsekort is a compound noun: helse (health) + kort (card).

Just like barn → barnet, you add the definite ending to say the health card:

et helsekort = a health card
helsekortet = the health card

So Barnet finner helsekortet … is specifically about the health card, not just a health card.

Why is helsekort written as one word and not helse kort?

Norwegian usually writes compound nouns as one word:

helse + kort → helsekort (health card)
sjokolade + kake → sjokoladekake (chocolate cake)

If you wrote helse kort as two words, it would sound like health short or health briefly, which doesn’t make sense. As one word, helsekort is a fixed term.

What does sitt mean, and why is it used here?

Sitt is a reflexive possessive pronoun meaning its/ his/ her (own), but it agrees in gender and number with the thing possessed, not with the owner.

Forms:

sin – with masculine/feminine singular nouns (e.g. boka sin)
sitt – with neuter singular nouns (e.g. brevet sitt)
sine – with plural nouns (e.g. bøkene sine)

Here, helsekort is neuter singular, so you use sitt:

Barnet finner helsekortet sitt.
→ The child finds its own health card.

What is the difference between sitt and hans/hennes in this sentence?

sitt = its/his/her own (reflexive, refers back to the subject)
hans = his (belongs to some male, not necessarily the subject)
hennes = her (belongs to some female, not necessarily the subject)

So:

Barnet finner helsekortet sitt.
→ The child finds its own health card.
Barnet finner helsekortet hans.
→ The child finds his health card (some other male person’s, not the child’s).
Barnet finner helsekortet hennes.
→ The child finds her health card (some other female person’s).

The reflexive sitt ties the card to the subject barnet.

Why does sitt come after helsekortet, not before it?

Norwegian possessives can appear before or after the noun, but:

After the noun (postposed) is common with reflexive forms like sin/sitt/sine, especially when the noun is definite.

Typical pattern:

helsekortet sitt = its (own) health card
boka si = her/ his own book

Putting sitt before the noun here (sitt helsekort) would sound odd and less natural in this exact sentence. For the reflexive and a definite noun, noun + definite ending + sin/sitt/sine is the normal pattern.

Could we leave out sitt and just say Barnet finner helsekortet?

Yes, grammatically you can, but the meaning changes slightly.

Barnet finner helsekortet.
→ The child finds the health card. (Context decides whose it is.)
Barnet finner helsekortet sitt.
→ The child finds its own health card (explicitly the child’s).

Without sitt, it’s less clear who the card belongs to. With sitt, it’s clearly the child’s.

How would the sentence change if we talked about children instead of the child?

Plural of barn is barn (same form), but the definite plural is barna:

barn – children
barna – the children

For the whole sentence:

Barna finner helsekortet sitt.
→ The children find their (own, shared) health card.
(One card that belongs to the group.)

If each child has their own card:

Barna finner helsekortene sine.
→ The children find their health cards.
(helsekortene = the health cards, plural; sine = reflexive plural.)

How is Barnet finner helsekortet sitt pronounced?

Approximate pronunciation in a standard East Norwegian accent (IPA):

Barnet → /ˈbɑːɳə/ or /ˈbɑːɳet/
finner → /ˈfɪnːər/
helsekortet → /ˈhɛlsəkɔʈə/ or /ˈhɛlsəkɔʈet/
sitt → /sɪt/

Main stress falls on the first syllable of each content word: BARN‑et FIN‑ner HEL‑se‑kort‑et sitt.