Den voksne passer på barna i hagen.

Voksen is an adjective meaning adult / grown-up.

In Norwegian, when an adjective is used with a definite noun, the adjective normally takes the -e ending (this is called the “weak” form):

• en voksen mann – an adult man (indefinite, no -e)
• den voksne mannen – the adult man (definite, adjective gets -e)

In your sentence, the noun person or mann/kvinne is understood and left out. So den voksne literally means the adult (person), where:

• den = the (for common gender)
• voksne = weak/definite form of voksen, used because the meaning is definite

So you get den voksne and not den voksen.

Normally, no.

You use:

• den with common gender nouns (en-words)
• det with neuter nouns (et-words)

Here den voksne means the adult person, and person / mann / kvinne are common gender nouns (en person, en mann, en kvinne). So you say den voksne.

You would use det voksne in front of a neuter noun, for example:

• det voksne barnet – the grown-up child (because barn is neuter: et barn)

But when voksne stands alone and means the adult (person), you use den voksne.

Å passe på is a verb + preposition expression that means:

• to look after, to watch, to take care of

Examples:

• Jeg passer på barna. – I look after the children.
• Kan du passe på vesken min? – Can you watch my bag?

Without på, å passe usually means things like:

• to fit (clothes)
• to suit / be suitable
• to be convenient

Examples without på:

• Buksen passer. – The trousers fit.
• Det passer dårlig. – That is a bad time / that doesn’t suit me.

So in your sentence, you need på to get the meaning look after:

• Den voksne passer på barna = The adult is looking after the children.
• Den voksne passer barna would normally not mean that; it sounds more like the adult suits the children (or is simply odd).

Barn is an irregular neuter noun:

• et barn – a child (singular, indefinite)
• barnet – the child (singular, definite)
• barn – children (plural, indefinite)
• barna – the children (plural, definite)

So:

• barna absolutely means the children.
• There is no -er ending in the plural; you don’t say barner.

In your sentence, barna is definite plural: the children the adult is responsible for.

Norwegian normally uses a definite form where English uses the:

• i hagen = in the garden / in the yard

The noun hage (garden/yard) has:

• en hage – a garden
• hagen – the garden

Because we’re talking about a specific garden (the one both speaker and listener know about, e.g. their garden), Norwegian uses the definite form: hagen.

So:

• i en hage – in a (random) garden
• i hagen – in the (known) garden

In Norwegian, i is used more for inside / within an area, while på is more on / on top of / at certain places.

A hage is thought of as an enclosed area, so you are in it:

• i hagen – in the garden

Compare:

• i huset – in the house
• i byen – in the city

You do use på with some other place words:

• på skolen – at school
• på kontoret – at the office
• på terrassen – on the terrace

But for a garden, the natural expression is i hagen.

The basic form (indefinite singular) is hage:

• en hage – a garden (common gender, en-word)
• hagen – the garden (definite singular)
• hager – gardens (indefinite plural)
• hagene – the gardens (definite plural)

In your sentence:

• i hagen = in the garden (definite singular).

This is the most natural, neutral word order:

1. Subject: Den voksne
2. Verb: passer
3. Object: på barna
4. Adverbial / place: i hagen

Norwegian main clauses follow a verb-second (V2) rule: the finite verb (here: passer) must be in second position.

You can move i hagen to the front for emphasis, but then the verb still has to be second:

• I hagen passer den voksne på barna. – In the garden, the adult is looking after the children.

You cannot do:

• *I hagen den voksne passer på barna. (wrong, because the verb is not in second position)

Norwegian has only one present tense form, used for both:

• simple present (looks after)
• present continuous / progressive (is looking after)

So passer på can mean both:

• The adult looks after the children in the garden.
• The adult is looking after the children in the garden.

Context usually makes it clear whether it is a habitual action or something happening right now; the verb form doesn’t change.

Approximate pronunciation (Central/Eastern Norwegian):

• voksne: VOKS-neh
  
  • voks-: like vox in English, with a short o
  • -ne: like neh
• barna: BAR-na
  
  • bar-: a bit like bar in English, but shorter vowel
  • -na: like nah
• hagen: HAH-gen
  
  • ha-: like ha in haha, long a
  • -gen: gen with a hard g (like in go)

Stress is on the first syllable of each word: VOKS-ne, BAR-na, HA-gen.