Barnet er sta.

Barn means child as an indefinite noun, while barnet means the child.

Norwegian usually adds the definite article to the end of the noun instead of putting a separate word in front:

barn = child
barnet = the child

So Barnet er sta means The child is stubborn.

The ending -et is the definite ending for many neuter nouns in Norwegian.

So here:

et barn = a child
barnet = the child

This is one of the first big differences from English: Norwegian often puts the at the end of the noun.

Yes. Barn is a neuter noun, so its indefinite article is et:

et barn = a child

That is why the definite singular form becomes barnet.

A useful thing to remember is that barn is also unusual because the plural indefinite is still barn:

et barn = a child
barn = children
barnet = the child
barna or barnene = the children

Er is the present tense of å være (to be).

So:

jeg er = I am
du er = you are
han/hun er = he/she is
barnet er = the child is

Unlike English, Norwegian does not change the present-tense form depending on the subject. It is always er.

Sta is an adjective. It describes barnet.

The structure is:

Barnet = subject
er = verb
sta = adjective describing the subject

This is very similar to English The child is stubborn, where stubborn also comes after is.

In this sentence, sta stays sta.

That is something learners often notice, because many Norwegian adjectives do change in some situations, but sta is commonly used in this unchanged form here:

Barnet er sta.

So for this sentence, the important thing is simply to learn sta as the adjective meaning stubborn.

It follows the normal Norwegian statement pattern:

subject + verb + complement

So:

Barnet + er + sta

This is the same basic order as English The child is stubborn.

A rough English-friendly pronunciation would be:

BAR-neht er stah

A few helpful notes:

• barn has a broad a sound, not the English air sound.
• In many natural pronunciations, the final -t in barnet is weak or not clearly pronounced.
• sta rhymes roughly with spa.

Pronunciation varies by dialect, but that approximation will help you get started.

Sometimes, yes. Sta usually means stubborn, but depending on context it can sound:

• negative: refusing to listen
• neutral: strong-willed
• slightly positive: determined

So if someone says Barnet er sta, it could mean the child is difficult and stubborn, but the exact tone depends on context and voice.

Yes, but the meaning changes:

Barnet er sta = The child is stubborn.
Et barn er sta = A child is stubborn.
Barn er sta = Children are stubborn / Children in general are stubborn.

So the sentence you were given is talking about one specific child.

Yes, it is completely natural.

It is short, simple, and idiomatic. Norwegian often uses short sentences like this in examples:

Barnet er trøtt. = The child is tired.
Barnet er glad. = The child is happy.
Barnet er sta. = The child is stubborn.

So this is a very normal pattern to learn from.