Barnet må spy.

Barn means child in general, or a child in some contexts.

Barnet means the child.
The ending -et is the definite article for many neuter nouns in Norwegian.

So:

• et barn = a child
• barnet = the child

This sentence uses barnet because it is talking about a specific child.

In Norwegian, the definite article is usually added to the end of the noun.

Compare:

• the child → barnet
• the house → huset
• the apple → eplet

This is a very normal pattern in Norwegian. English uses a separate word (the), but Norwegian often uses a noun ending instead.

Må is the present tense of måtte, and it usually means must, have to, or sometimes need to.

In this sentence, it expresses necessity:

• Barnet må spy. = The child must throw up / needs to vomit.

Depending on context, må can sound like:

• strong obligation: must
• practical necessity: has to
• obvious need: needs to

After a modal verb like må, Norwegian uses the infinitive form of the main verb.

So:

• må spy = must vomit
• kan komme = can come
• vil spise = will eat / wants to eat
• skal gå = will / shall go

The verb spy is the infinitive here. You do not conjugate it after må.

Spy is a common everyday verb meaning to vomit / to throw up.

It is fairly natural in spoken language and not especially formal.
Depending on the situation, Norwegian also has other words, for example:

• kaste opp = throw up
• brekke seg = retch / gag
• vomitere = vomit (more formal/medical, less common in ordinary speech)

So spy is normal and useful to know.

Spy is pronounced approximately like spew in English, but the exact vowel quality is Norwegian.

A rough guide:

• sp as in English spill
• y is a Norwegian vowel that does not exist exactly in standard English

If you are learning pronunciation, the most important point is that y in Norwegian is not the same as English y in yes.

Barn is a neuter noun.

That is why it takes:

• et barn = a child
• barnet = the child

This is important because Norwegian noun gender affects articles and adjective endings.

This is a normal Norwegian main clause:

• Subject: Barnet
• Finite verb: må
• Infinitive: spy

So the structure is:

Subject + finite verb + infinitive

This is very common with modal verbs:

• Jeg må gå. = I must go.
• Hun kan svømme. = She can swim.
• Vi vil spise. = We want to eat.

Yes, but the meaning changes.

• Barnet må spy. = The child must throw up.
  A specific child.

• Et barn må spy. = A child must throw up.
  An unspecified child.

So both are grammatical, but they do not mean the same thing.

Yes, in some contexts må can express logical conclusion, like must in English:

• Han må være hjemme. = He must be at home.

But in Barnet må spy, the most natural reading is physical necessity or immediate need: the child needs to vomit.

So here it is not mainly about deduction; it is about necessity.

Yes. Må is a modal verb, and modal verbs often behave a bit differently from ordinary verbs.

A few useful points:

• It is followed by an infinitive: må spy
• It does not take å before the infinitive:
  • må spy, not må å spy
• It is very common in everyday Norwegian

That missing å is important, because English speakers often expect something like to before the second verb.

No. That would be incorrect.

After må, you use the infinitive without å:

• Barnet må spy. ✅
• Barnet må å spy. ❌

This is the same pattern as with other modal verbs:

• Jeg kan svømme. ✅
• Hun vil spise. ✅
• Vi skal dra. ✅

Here, barnet is clearly singular definite: the child.

You are right that barn can be tricky, because the indefinite singular and the plural base form look the same:

• et barn = a child
• barn = children (in many contexts)
• barnet = the child
• barna / barnene = the children (depending on variety/style)

So the ending -et helps show that this sentence is about one specific child.

Yes. It is short, natural, and completely understandable.

A speaker might also say things like:

• Barnet må kaste opp.
• Barnet holder på å spy. = The child is about to throw up.
• Barnet kommer til å spy. = The child is going to throw up.

But Barnet må spy itself is a normal sentence.