Det som barnen åt först var melon, men sedan ville de också ha hallon och blåbär.

Det som is a very common Swedish pattern meaning something like the thing that, what, or that which.

So:

• Det som barnen åt först = What the children ate first / The thing that the children ate first

In Swedish, this structure is often more natural than trying to copy English directly. Here, det does not mean a specific it in the usual sense; it helps build the phrase det som ....

Barnen is the definite plural form of barn.

• ett barn = a child
• barn = children / child (the word has the same basic form in singular indefinite and plural indefinite)
• barnen = the children

So barnen åt först means the children ate first or, in this sentence, the children ate first as part of the relative clause.

Åt is the past tense of äta (to eat).

• äta = to eat
• äter = eat / is eating
• åt = ate
• ätit = eaten

So:

• barnen åt först = the children ate first

This sentence is talking about a past event, so åt is the correct form.

Först means first, and in Swedish adverbs often come after the verb in simple clauses.

So:

• barnen åt först = the children ate first

That word order is normal and natural in Swedish. English sometimes places adverbs more flexibly, but Swedish often prefers this kind of placement.

Here melon is being used more like a food item or substance, not as one whole melon.

So:

• var melon = was melon
• var en melon would suggest was a melon, meaning one individual melon

In food contexts, Swedish often leaves out the article when talking about what something was, what someone ate, or what was served:

• Det var soppa. = It was soup.
• Vi åt fisk. = We ate fish.

So var melon sounds natural if the point is the type of food, not one countable object.

The first part, Det som barnen åt först, functions as a single unit at the start of the sentence. After that comes the verb var.

This is normal Swedish word order:

• Det som barnen åt först = subject-like phrase
• var = was
• melon = complement

So the structure is basically:

• What the children ate first was melon

Even though the opening part is long, it still counts as the thing the sentence is about, so var comes right after it.

Sedan means then, after that, or later.

In this sentence:

• men sedan ville de också ha ... = but then/after that they also wanted ...

Sedan and sen are very close in meaning.

• sedan = slightly more formal or full form
• sen = very common in speech and informal writing

So you could also hear:

• men sen ville de också ha ...

Both are correct in many situations.

This is because of the V2 rule in Swedish: in main clauses, the finite verb usually comes in the second position.

Here, the sentence after men begins with sedan:

• first position: sedan
• second position: ville
• then: de också ha

So:

• Sedan ville de också ha ...

If there were no starting adverb, you would get:

• De ville också ha ...

This is one of the most important Swedish word-order rules.

In ville de också ha hallon och blåbär, också modifies the idea of also wanted to have.

Word order with adverbs in Swedish can be tricky, but this placement is very natural:

• ville de också ha = did they also want to have

You will often see adverbs like också, inte, alltid, etc. placed after the subject in this kind of clause.

Compare:

• Sedan ville de också ha hallon.
• Sedan ville de inte ha hallon.

So också comes in a normal adverb position here.

Yes, ha literally means have, but in Swedish it is also commonly used where English would say want plus the thing directly, especially with food.

So:

• ville de också ha hallon och blåbär literally = they also wanted to have raspberries and blueberries
• natural English = they also wanted raspberries and blueberries

Swedish often says vill ha where English simply says want:

• Jag vill ha kaffe. = I want coffee.
• Hon vill ha glass. = She wants ice cream.

So this is a very useful everyday pattern.

For the same reason as with melon: these are food items being mentioned in a general sense, not specific individually counted objects.

• hallon = raspberries
• blåbär = blueberries

In Swedish, when talking about food in general, articles are often omitted:

• Jag äter äpple.
• Vi köpte jordgubbar.
• De ville ha hallon och blåbär.

If you wanted to be more specific, you could add other words, such as:

• några hallon = some raspberries
• ett hallon = a raspberry

But in this sentence, the article-less form is the natural choice.

Here hallon is best understood as plural or as an uncounted food item, depending on context.

A tricky point is that hallon has the same form in singular and plural indefinite:

• ett hallon = a raspberry
• hallon = raspberries

So in a phrase like ha hallon, it usually means have/eat raspberries in a general sense.

This is similar to some other Swedish neuter words where singular and plural can look the same.

A helpful breakdown is:

• Det som barnen åt först = what the children ate first
• var melon = was melon
• men sedan = but then / but after that
• ville de också ha hallon och blåbär = they also wanted raspberries and blueberries

So the sentence has two main parts joined by men:

1. Det som barnen åt först var melon
2. sedan ville de också ha hallon och blåbär

The first part identifies the first food item.
The second part tells us what they wanted after that.

Yes. A more direct version might be:

• Barnen åt först melon, men sedan ville de också ha hallon och blåbär.

This means nearly the same thing. The original sentence with Det som ... var ... puts extra focus on melon:

• Det som barnen åt först var melon = What the children ate first was melon

So the original is a bit more focused or explanatory, while the simpler version is more neutral.