Die Mutter tröstet das Kind, weil es vor der lauten Sirene Angst hat.

Because trösten takes a direct object in the accusative case.

• die Mutter = the mother → subject
• tröstet = comforts
• das Kind = the child → direct object

So:

• Die Mutter tröstet das Kind. = The mother comforts the child.

If it were dem Kind, that would be dative, but trösten does not normally take a dative object here.

Es refers to das Kind.

That is because Kind is a neuter noun in German:

• das Kind → es

Even if the child is a boy or a girl in real life, the pronoun often follows the grammatical gender of the noun:

• das Kind → es

So in this sentence, weil es ... Angst hat means because it/the child is afraid ...

Because weil introduces a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

Main clause:

• Die Mutter tröstet das Kind

Subordinate clause:

• weil es vor der lauten Sirene Angst hat

So:

• weil = because
• German word order after weil pushes the verb to the end
• That is why you get ... Angst hat, not ... hat Angst

This is one of the most important German word order patterns to learn.

Because in German, a subordinate clause introduced by weil is separated from the main clause by a comma.

So this is standard punctuation:

• Die Mutter tröstet das Kind, weil es vor der lauten Sirene Angst hat.

The comma is required, not optional.

German uses the expression Angst haben vor + dative to mean to be afraid of something.

So:

• Angst haben vor etwas = to be afraid of something

That is why the sentence says:

• vor der lauten Sirene

Here vor takes the dative case in this expression.

Since Sirene is feminine:

• nominative: die Sirene
• dative: der Sirene

So vor der Sirene means of/from the siren in the sense of afraid of the siren.

Because the adjective laut is describing Sirene, and it must take the correct adjective ending.

The phrase is:

• vor der lauten Sirene

Here:

• der = dative feminine singular
• after a definite article in dative feminine, the adjective takes -en

So:

• die laute Sirene = nominative
• vor der lauten Sirene = dative after vor

This is a normal adjective ending pattern.

Because German commonly expresses this idea with the noun Angst plus the verb haben.

• Angst haben = to be afraid
• literally: to have fear

So:

• es hat Angst = it is afraid

This is a very common German structure. English often prefers an adjective or verb, but German often uses Angst haben.

Also, Angst is capitalized because all German nouns are capitalized.

Yes. That version is also correct.

You can say:

• weil es vor der lauten Sirene Angst hat
• weil es Angst vor der lauten Sirene hat

Both mean the same thing.

The difference is mainly word order inside the clause. German often allows some flexibility in the middle of the sentence, as long as the verb still stays at the end in a subordinate clause.

The original version sounds very natural.

Because die Mutter is the subject of the sentence, so it is in the nominative case.

• die Mutter = nominative singular
• der Mutter would be dative or genitive singular

Since the mother is the one doing the action, German uses nominative:

• Die Mutter tröstet ...

It is in the present tense.

• tröstet = comforts / is comforting
• hat Angst = is afraid

In German, the present tense is often used where English might use either:

• comforts
• is comforting

depending on context.

So the German present tense is very flexible here.

In this sentence, the most natural interpretation is that es refers to das Kind.

Why?

• die Mutter would normally become sie
• das Kind becomes es

So grammatically, es points to das Kind.

In real conversation, context always helps too, but here the grammar already makes the reference quite clear.

It has two parts:

1. Main clause

   • Die Mutter tröstet das Kind
   • subject + verb + object

2. Subordinate clause introduced by weil

   • weil es vor der lauten Sirene Angst hat
   • conjunction + subject + other elements + verb at the end

So the pattern is:

• [main clause], weil [subordinate clause].

This is a very common German sentence pattern.