Mostern frågade om barnen ville ha mer blåbär.

Moster means aunt, specifically your mother’s sister.

Mostern is the definite singular form, so it means the aunt.

This is a common Swedish pattern:

• en moster = an aunt
• mostern = the aunt

A useful extra detail: Swedish makes a distinction that English usually does not:

• moster = mother’s sister
• faster = father’s sister

So mostern is not just any aunt; it is specifically the maternal aunt.

Frågade is the past tense of fråga (to ask).

• fråga = to ask
• frågar = asks / is asking
• frågade = asked

So Mostern frågade means The aunt asked.

Here, om means if or whether.

It introduces an indirect yes/no question:

• Mostern frågade om barnen ville ha mer blåbär. = The aunt asked if the children wanted more blueberries.

This is different from another common meaning of om, which is about.

For example:

• Hon frågade om vädret. = She asked about the weather.
• Hon frågade om barnen ville ha mer blåbär. = She asked if the children wanted more blueberries.

So the meaning depends on what comes after om.

Because this is an indirect question, not a direct question.

In a direct question, Swedish uses inversion:

• Ville barnen ha mer blåbär? = Did the children want more blueberries?

But after om, it becomes an embedded clause, and Swedish uses normal subject-verb order:

• ... om barnen ville ha mer blåbär = ... if the children wanted more blueberries

So:

• direct question: Ville barnen ... ?
• indirect question: om barnen ville ...

This is very similar to English:

• direct: Did the children want more blueberries?
• indirect: She asked if the children wanted more blueberries.

Barnen is the definite plural form of barn.

• ett barn = a child
• barn = children
• barnen = the children

A thing learners often notice is that barn has the same form in the indefinite singular and indefinite plural:

• ett barn = a child
• två barn = two children

Then -en is added for the definite plural:

• barnen = the children

Because ha is part of the meaning here.

Literally, ville ha means wanted to have, but in natural English it is often translated more simply as:

• wanted
• wanted some
• would like

With food, drink, or things being offered, Swedish often uses vilja ha:

• Vill du ha kaffe? = Do you want coffee? / Would you like coffee?
• Barnen ville ha mer blåbär. = The children wanted more blueberries.

So ville ha is a very normal Swedish way to talk about wanting food or something to receive/have.

Because vilja is a modal verb, and modal verbs in Swedish are followed by the bare infinitive—that is, the infinitive without att.

So you say:

• vill ha = want to have
• kan komma = can come
• ska gå = will/go
• måste läsa = must read

Not:

• vill att ha ❌

So ville ha is correct because ha follows the modal verb ville.

This is a very natural question, because English uses more for both countable and uncountable nouns.

In Swedish:

• mer is usually used for more in quantity/amount
• fler is used for more in number

With food, Swedish often prefers mer, even when the noun could in theory be counted:

• mer blåbär = more blueberries / more blueberry stuff / a larger amount of blueberries

If you were focusing strictly on the number of individual berries, fler blåbär could make sense. But in a sentence about serving or eating food, mer blåbär sounds very natural.

So here mer blåbär is the expected choice.

In form, blåbär can be singular or plural, depending on context.

• ett blåbär = a blueberry
• två blåbär = two blueberries

The noun does not change in the plural indefinite form, just like barn.

In this sentence, the meaning is clearly plural/general quantity:

• mer blåbär = more blueberries

So even though the form looks the same as the singular, the context tells you it is plural or mass-like in meaning.

Primarily, ville is the past tense of vilja (to want), so the core meaning is wanted.

But in context, especially with food or offers, English may translate it a bit more naturally as:

• wanted
• would like

So:

• barnen ville ha mer blåbär can be understood as
  • the children wanted more blueberries
  • or, in a slightly smoother context-based translation, the children would like more blueberries

The Swedish form itself is just the normal past tense ville.

Yes. A direct question would be:

• Ville barnen ha mer blåbär? = Did the children want more blueberries?

The sentence you have is the reported/embedded version:

• Mostern frågade om barnen ville ha mer blåbär. = The aunt asked if the children wanted more blueberries.

So this is a very useful pattern to learn:

• direct question: Ville barnen ... ?
• reported question: frågade om barnen ville ...

That change in word order is one of the key grammar points in the sentence.