Learn Hardcore German: Die Kinder streiten sich leise im Flur, weil beide das gleiche Spielzeug wollen. - The children argue quietly in the hallway because both want the same toy.

streiten on its own usually means to dispute, to fight (about something) in a more general sense, often with an object:
- Sie streiten das Ergebnis ab. – They dispute the result.
sich streiten focuses on the people arguing with each other:
- Die Kinder streiten sich. – The children are arguing (with each other).

So in this context, Die Kinder streiten sich is the natural idiomatic way to say The children are arguing.

What exactly does the reflexive pronoun sich refer to here, and why that form?

The reflexive pronoun sich refers back to the subject die Kinder.

Subject: die Kinder → 3rd person plural
3rd person plural reflexive pronoun (accusative): sich

Reflexive pronouns in the accusative:

ich → mich
du → dich
er/sie/es → sich
wir → uns
ihr → euch
sie/Sie → sich

Because die Kinder = sie (3rd person plural), the correct reflexive form is sich.

Why is it leise and not something like leisen or leisem?

Leise here is an adverb, not an adjective in front of a noun.

With verbs, German usually uses the basic adjective form as an adverb:
- Sie sprechen leise. – They speak quietly.
- Er läuft schnell. – He runs quickly.
Adjective endings like -e, -en, -em are used only when the adjective directly describes a noun:
- die leise Stimme – the quiet voice
- im leisen Flur – in the quiet hallway

In streiten sich leise, leise answers How are they arguing? → It behaves as an adverb → no extra ending.

Can the word order leise im Flur be changed? For example: im Flur leise?

Yes, both are grammatically possible, but there are tendencies:

Usual order for adverbials in German is Manner – Place – Time:
- Die Kinder streiten sich leise im Flur.
  - Manner: leise
  - Place: im Flur

If you say:

Die Kinder streiten sich im Flur leise.

it is still correct, but sounds a bit less neutral and can put a slight emphasis on leise (as if contrasting with another way of arguing).

For a neutral sentence, leise im Flur fits the usual pattern and sounds very natural.

Why is there a comma before weil, and why does wollen go to the end?

Weil introduces a subordinate clause (Nebensatz) that expresses the reason.

Comma: In German, a comma is always used between a main clause and a subordinate clause:
- Die Kinder streiten sich leise im Flur, weil ...
Verb at the end: In subordinate clauses introduced by weil, the finite verb goes to the end:
- ..., weil beide das gleiche Spielzeug wollen.
- Subject: beide
- Object: das gleiche Spielzeug
- Finite verb: wollen → at the end

So both the comma and the final verb position are regular features of weil-clauses.

Why is it wollen and not will or some other form?

The verb wollen must agree with its subject in person and number.

Subject: beide (referring to the two children) → 3rd person plural
Conjugation of wollen in the present:
- ich will
- du willst
- er/sie/es will
- wir wollen
- ihr wollt
- sie/Sie wollen

For sie (they) / beide, the correct form is wollen.

So:
..., weil beide das gleiche Spielzeug wollen.

What does beide mean here exactly, and why is it alone without sie?

Beide means both and refers to the two children mentioned earlier.

We know from Die Kinder that there are at least two children.
beide here functions as the subject of the subordinate clause:
- ..., weil beide das gleiche Spielzeug wollen.
  → Because both want the same toy.

You could also say:

..., weil sie beide das gleiche Spielzeug wollen.

Both versions are correct. The version without sie is slightly more compact. Beide alone can act as a pronoun when the reference is clear from context.

Why is it das gleiche Spielzeug and not something like den gleichen Spielzeug?

The form depends on the gender and case of the noun Spielzeug.

Spielzeug is neuter in German:
- das Spielzeug (Nom. / Acc. singular)
In the clause weil beide das gleiche Spielzeug wollen, das gleiche Spielzeug is the direct object of wollen, so it is in the accusative.
For neuter accusative singular with a definite article, the article is das, and the adjective ending is -e:
- das gleiche Spielzeug

Pattern:
das + adjective → adjective gets -e in neuter nominative and accusative singular:

das neue Auto
das gleiche Spielzeug

Den would be accusative for masculine nouns, e.g.:

den gleichen Ball (Ball = masculine)

What is the difference between das gleiche and dasselbe?

Both can be translated as the same, but they are used differently:

das gleiche Spielzeug
→ the same kind of toy, an identical toy, but not necessarily the very same physical object
dasselbe Spielzeug
→ the exact same physical toy, one single object that both want

Example:

Wir haben das gleiche Auto.
→ We have the same model of car (two different cars, but identical).
Wir fahren dasselbe Auto.
→ We drive the very same car (one car, shared).

In everyday speech, many native speakers mix them, but the distinction above is the traditional, precise one.

Why is it im Flur and not in dem Flur?

Im is a standard contraction of in dem:

in (preposition) + dem (dative article, masculine/neuter) → im

Since Flur is masculine:

Dative singular masculine: dem Flur
So in dem Flur → im Flur

Both im Flur and in dem Flur are grammatically correct, but in normal speech and writing im Flur is much more common and sounds more natural.

Is im Flur dative, and why is dative used with in here?

Yes, im Flur is dative.

The preposition in can take either dative or accusative, depending on the meaning:

Dative → location (Where?)
- Die Kinder sind im Flur. – They are in the hallway.
Accusative → direction/movement (Where to?)
- Die Kinder gehen in den Flur. – They go into the hallway.

In the sentence, im Flur answers Where are they arguing?, which is a location → therefore dative.

Could (or should) it be streiten sich um das gleiche Spielzeug instead of using wollen?

Both are possible, but they mean slightly different things:

Die Kinder streiten sich leise im Flur, weil beide das gleiche Spielzeug wollen.
- Focus: They both want the same toy.
- The reason for the argument is their desire.
Die Kinder streiten sich leise im Flur um das gleiche Spielzeug.
- Here um etwas streiten means to argue about something.
- Focus: The topic or object of the argument is that toy.

Your original sentence combines sich streiten with a weil-clause explaining the cause. Using um is another common pattern, but it changes the structure: the reason is then built into the main clause instead of a separate weil-clause.

How would this sentence translate in terms of tense? Is it more like are arguing or argue?

German does not have a separate present progressive form (are arguing). The Präsens covers both:

Die Kinder streiten sich leise im Flur ...
- The children are arguing quietly in the hallway ...
- or The children argue quietly in the hallway ...

In normal context, the most natural English translation here is:

The children are arguing quietly in the hallway, because both want the same toy.

So German streiten sich in the present → English present simple argue or present progressive are arguing, depending on context.

Is the sentence still correct if I change the second part to weil sie beide das gleiche Spielzeug wollen?

Yes, that is absolutely correct:

Die Kinder streiten sich leise im Flur, weil sie beide das gleiche Spielzeug wollen.

Here:

sie = they (the children)
beide = both

sie beide is a bit more explicit, reinforcing that both of them want it. The original weil beide das gleiche Spielzeug wollen is slightly shorter and more compact, but the meaning is the same in this context.