Børnene skal opføre sig roligt i venteværelset, især når der sidder andre patienter der.

Børnene means the children, while børn means children in a general or indefinite sense.

Danish often adds the definite article as an ending:

• barn = a child
• barnet = the child
• børn = children
• børnene = the children

So Børnene skal... means we are talking about specific children, not children in general.

Here skal expresses obligation or what is expected: must / are supposed to / should.

So Børnene skal opføre sig roligt means the children are expected to behave calmly.

A few useful comparisons:

• skal = must / have to / are supposed to
• må = may / be allowed to / sometimes must, depending on context
• bør = ought to / should

In this sentence, skal sounds like a rule or instruction.

Opføre sig is a fixed reflexive expression meaning to behave.

The word sig is the reflexive pronoun, like oneself in English, though in English we usually do not say behave oneself every time.

Examples:

• Han opfører sig pænt. = He behaves well.
• Børnene opfører sig roligt. = The children behave calmly.

You normally need sig with this verb when the subject is third person:

• jeg opfører mig
• du opfører dig
• han/hun/den/det opfører sig
• vi opfører os
• I opfører jer
• de opfører sig

So in this sentence, sig is not optional.

Because roligt is being used as an adverb, not as an adjective.

It describes how the children should behave:

• rolig = calm
• roligt = calmly

Compare:

• et roligt barn = a calm child
• barnet er roligt = the child is calm
• barnet opfører sig roligt = the child behaves calmly

In the sentence, roligt modifies the action opføre sig, so the adverb form is needed.

Venteværelset is a compound noun:

• vente = waiting
• værelse = room
• venteværelse = waiting room

The ending -et makes it definite:

• et venteværelse = a waiting room
• venteværelset = the waiting room

This is very common in Danish. Instead of putting a separate word for the in front, Danish often adds the definite article to the end of the noun.

Når is used for when in general, repeated, or expected situations.

Here the meaning is something like: the children should behave calmly, especially when other patients are there.

Useful contrast:

• når = when, in situations that happen regularly or generally
• da = when, for a specific event in the past
• hvis = if

Examples:

• Når jeg er træt, drikker jeg kaffe. = When I am tired, I drink coffee.
• Da jeg var barn, boede jeg i Odense. = When I was a child, I lived in Odense.
• Hvis det regner, bliver vi hjemme. = If it rains, we stay home.

So når fits because this is a general rule, not one single past event.

The two der words do different jobs.

1. The first der is a dummy or expletive subject.
   It is used in Danish in sentences like there is / there are:

   • Der sidder andre patienter... = There are other patients sitting...

2. The second der means there, referring to the place, here the waiting room:

   • ...andre patienter der = ...other patients there

So:

• first der = grammatical subject placeholder
• second der = adverb of place

This is very normal in Danish, even though it can look strange to an English speaker.

Danish often uses posture verbs where English simply uses be.

Here sidder literally means sit / are sitting, and it suggests that the patients are seated in the waiting room.

So:

• der sidder andre patienter der = there are other patients sitting there

In natural English, we often just say there are other patients there, but Danish commonly prefers a more physical verb such as:

• sidde = sit
• stå = stand
• ligge = lie
• hænge = hang

This makes Danish sound more concrete about position.

Both grammar and nuance are involved.

With der sidder andre patienter der, Danish uses an existential structure, similar to there are other patients sitting there. This introduces the existence/presence of other patients.

If you say når andre patienter sidder der, that means when other patients are sitting there, which is grammatically possible, but it puts andre patienter more directly as the subject rather than using the existential there are type of structure.

The version in the sentence sounds very natural because the point is the presence of other patients in the waiting room, not specifically what those patients are doing.

Især means especially.

It highlights the second part of the sentence:

• The children should behave calmly in the waiting room in general.
• This is even more important especially when there are other patients there.

So især adds emphasis rather than changing the basic grammar.