I simhallen måste barnen vänta på mig utanför omklädningsrummet.

This is because Swedish main clauses follow the V2 rule: the finite verb must come in the second position.

• First position: I simhallen
• Second position: måste
• Then the subject: barnen

So when a place phrase comes first, the verb moves before the subject.

Compare:

• Barnen måste vänta... = normal subject-first order
• I simhallen måste barnen vänta... = place phrase first, so verb comes before the subject

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

Swedish uses i for being in or inside an enclosed place, and also often where English would naturally say at.

So i simhallen can mean:

• physically in the swimming facility
• idiomatically at the pool / at the swimming baths

A simhall is usually an indoor public swimming facility, so i is the natural preposition here.

Simhallen is the definite form of simhall.

• sim = swim
• hall = hall

But the full meaning is not just a literal hall. In everyday Swedish, simhall usually means an indoor public swimming pool / swimming facility / swimming baths.

So simhallen means the swimming pool building/facility.

Because barnen is the definite plural form: the children.

Here are the forms:

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

So the sentence is talking about specific children, not just children in general.

In Swedish, definiteness is usually added as an ending on the noun instead of using a separate word like English the.

Examples from the sentence:

• simhall → simhallen = the swimming facility
• barn → barnen = the children
• omklädningsrum → omklädningsrummet = the changing room

So Swedish often builds the directly into the noun.

Because måste is a modal verb, and modal verbs are followed directly by the infinitive form of the next verb.

So you get:

• måste vänta = must wait
• kan simma = can swim
• vill gå = want to go
• ska äta = will / is going to eat

After these verbs, you normally do not use att.

In Swedish, when you say you are waiting for someone or something, you normally use vänta på.

So:

• Jag väntar. = I am waiting.
• Jag väntar på dig. = I am waiting for you.
• Jag väntar på bussen. = I am waiting for the bus.

So på is part of the normal pattern when the person or thing being waited for is named.

Because after a preposition like på, Swedish uses the object form of the pronoun.

• jag = I
• mig = me

So:

• Jag väntar = I am waiting
• Barnen väntar på mig = The children are waiting for me

This is similar to English:

• I wait
• They wait for me

Omklädningsrummet means the changing room.

It is a compound noun:

• omklädning = changing clothes
• linking -s-
• rum = room

Together:

• omklädningsrum = changing room
• omklädningsrummet = the changing room

This is very typical Swedish: long compound nouns are common, and they are often easier to understand once you break them into parts.

Here utanför means outside and works as a preposition.

So:

• utanför omklädningsrummet = outside the changing room

You can also use utanför without a following noun:

• Barnen väntar utanför. = The children are waiting outside.

In this sentence, the noun is included, so it specifies exactly where outside.

Because the sentence refers to a specific changing room, the one relevant in that situation.

Swedish often uses the definite form when both speaker and listener can identify the place from context.

So utanför omklädningsrummet means not just outside a changing room, but outside the changing room that matters here.

It can mean either, depending on context.

Måste often covers both:

• must
• have to
• need to

So this sentence could mean:

• the children are required to wait outside
• the children need to wait outside for practical reasons

The exact force depends on the situation, not on the grammar alone.

Grammatically, måste is in the present tense, but Swedish present tense often covers both present and future meaning.

So the sentence can mean:

• a general rule
• something that is true now
• something that will happen in that situation

For example, it could mean that whenever the speaker is in the swimming facility, the children have to wait outside the changing room.