Om det inte regnar, vill barnen åka rutschkana på lekplatsen.

Om means if here. It introduces a condition:

• Om det inte regnar = If it doesn’t rain

This is a very common way to form conditional sentences in Swedish.

Be aware that om can also mean whether in other contexts, but in this sentence it clearly means if.

In Swedish, weather expressions usually use det as a dummy subject, just like English uses it:

• Det regnar = It is raining
• Det snöar = It is snowing

So det does not refer to a specific thing. It is just required grammatically.

This is because Om det inte regnar is a subordinate clause.

In Swedish subordinate clauses, sentence adverbs like inte usually come before the finite verb:

• ... att han inte kommer
• ... om det inte regnar

In a main clause, inte usually comes after the finite verb:

• Det regnar inte

So the word order changes because of the clause type.

This is a classic Swedish word order rule: Swedish is a V2 language, meaning the finite verb normally comes in the second position of a main clause.

The sentence begins with the conditional clause:

• Om det inte regnar,

After that, the main clause starts. Because something else has taken the first position, the finite verb must come next:

• vill barnen åka rutschkana på lekplatsen

So:

• Om det inte regnar, vill barnen ... = correct
• Om det inte regnar, barnen vill ... = incorrect

Compare:

• Barnen vill åka rutschkana = The children want to go on the slide
• Om det inte regnar, vill barnen åka rutschkana = If it doesn’t rain, the children want to go on the slide

Barnen is the definite plural form of barn:

• ett barn = a child
• barn = children / child(ren) in indefinite plural
• barnen = the children

So the ending -en here marks definiteness: the children.

After the modal verb vill (want to), Swedish uses the infinitive without att:

• Jag vill gå = I want to go
• De vill äta = They want to eat
• Barnen vill åka rutschkana = The children want to go on the slide

This is similar to English, which also says want to go, not want that go.

Åka rutschkana is an idiomatic Swedish expression meaning to go down the slide or to ride the slide.

Parts of it:

• åka = go/ride/travel
• rutschkana = slide

Even though English often says go on the slide or go down the slide, Swedish commonly uses åka rutschkana.

So this is a fixed, natural expression, not something you should translate word-for-word too mechanically.

Rutschkana is a compound noun:

• rutsch relates to sliding
• kana can mean a track or chute

Together, rutschkana means slide in the playground sense.

Swedish forms many nouns this way by combining smaller words into one compound.

På lekplatsen means at the playground or sometimes on the playground, depending on context.

Parts:

• på = on / at
• lekplatsen = the playground

Swedish often uses på with places where English might also use at:

• på lekplatsen = at the playground
• på jobbet = at work
• på stranden = at the beach

So på is the natural preposition here.

Because lekplatsen is the definite singular form of lekplats:

• en lekplats = a playground
• lekplatsen = the playground

In Swedish, definiteness is often shown by adding an ending to the noun rather than using a separate word like the.

So:

• på en lekplats = at a playground
• på lekplatsen = at the playground

Regnar is the present tense of regna (to rain):

• regna = to rain
• regnar = rains / is raining

In Swedish, the present tense often covers both simple present and present progressive meanings:

• Det regnar = It rains / It is raining

In this sentence, English usually prefers doesn’t rain:

• Om det inte regnar = If it doesn’t rain

Yes, absolutely.

This version is also correct:

• Barnen vill åka rutschkana på lekplatsen om det inte regnar.

The difference is mainly emphasis and sentence structure:

• Om det inte regnar, vill barnen ... puts the condition first
• Barnen vill ... om det inte regnar states the main idea first and adds the condition afterward

Both are natural Swedish. The first version is a little more focused on the condition.