Learn Hardcore German: Die Kinder sitzen ruhig im Klassenzimmer. - The children sit quietly in the classroom.

feminine singular nominative/accusative: die Frau (the woman)
all plurals nominative/accusative: die Kinder, die Männer, die Frauen (the children, the men, the women)

The singular of Kinder is das Kind (neuter), but in the plural, all genders use die:

das Kind → die Kinder (the child → the children)
der Hund → die Hunde (the dog → the dogs)
die Frau → die Frauen (the woman → the women)

So it’s die Kinder because it’s plural, not because of gender.

Why is it Kinder and not Kindern?

Kinder is in the nominative plural, because it is the subject of the sentence (the ones doing the sitting).

Kindern is the dative plural and would be used, for example:

Ich spreche mit den Kindern.
(I’m talking with the children.)
Ich helfe den Kindern.
(I help the children.)

In our sentence:

Wer sitzt ruhig? (Who is sitting quietly?) → Die Kinder.
So nominative → die Kinder, not den Kindern.

Why is the verb sitzen and not something like sind?

Sitzen is a full verb meaning to sit, describing a position.
Sein (sind) is the verb to be, usually linking subject and description.

Die Kinder sitzen ruhig.
The children are sitting quietly. (emphasis: they are in a sitting position)
Die Kinder sind ruhig.
The children are quiet/calm. (emphasis: their behavior/state, not the posture)

So sitzen conveys where/how they are positioned; sind ruhig just describes them as calm/quiet, regardless of position.

Why does sitzen look like the infinitive? Shouldn’t it change in the present tense?

For regular verbs, the 3rd person plural form in the present tense is the same as the infinitive.

Infinitive: sitzen
Conjugation (present):

ich sitze
du sitzt
er/sie/es sitzt
wir sitzen
ihr sitzt
sie/Sie sitzen

So for sie (they), the form is sitzen, identical to the infinitive, but it is a conjugated verb here:
Die Kinder sitzen … = They sit / They are sitting …

How do I translate the tense? Is it “The children sit” or “The children are sitting”?

German has one present tense that usually covers both:

Die Kinder sitzen ruhig im Klassenzimmer.
- The children sit quietly in the classroom.
- The children are sitting quietly in the classroom.

Both English versions are correct translations; context decides which sounds more natural. In everyday English, “are sitting” is more common here.

What exactly is ruhig doing here? Is it an adjective or an adverb?

In German, the form of many adjectives and adverbs is the same. Ruhig can be:

Adjective:
- ein ruhiges Klassenzimmer (a quiet classroom)
- das ruhige Kind (the calm child)
Adverb (how they sit):
- Die Kinder sitzen ruhig. (The children sit quietly / are sitting quietly.)

In our sentence, ruhig describes how they sit → it functions adverbially.
German does not add an -ly equivalent; you just use the bare adjective form as an adverb.

What’s the difference between ruhig, still, and leise?

All three can relate to quietness, but they’re not identical:

ruhig
- calm, not restless, not noisy or disruptive
- can describe both noise level and behavior/state
- Die Kinder sind ruhig. (The children are calm/quiet.)
still
- very quiet, still, often with a sense of very little movement or sound
- Sei still! (Be quiet! often more strict/commanding)
leise
- low volume, not loud (whispering, soft voices, etc.)
- mainly about sound level
- Die Kinder sprechen leise. (The children speak quietly/softly.)

In Die Kinder sitzen ruhig, the focus is on calm, non-disruptive behavior while sitting.

What does im mean, and why isn’t it in dem Klassenzimmer?

im is a contraction of:

in + dem → im

So:

in dem Klassenzimmer = im Klassenzimmer

Both are grammatically correct, but in modern German, the contracted form is much more common in speech and writing:

im (in dem), am (an dem), zum (zu dem), vom (von dem), etc.

Here:

im Klassenzimmer = in the classroom
(dative case: dem Klassenzimmer)

Why does in here take the dative (im) and not the accusative?

in is a two-way preposition (Wechselpräposition). It can take:

dative: for a location / no movement
accusative: for a direction / movement into

Examples:

Ich bin in dem Klassenzimmer. (location → dative)
Ich gehe in das Klassenzimmer. (movement into → accusative)

In our sentence:

The kids are located in the classroom, not moving into it → dative.
So: in dem Klassenzimmer → im Klassenzimmer.

What gender is Klassenzimmer, and how do I know?

Klassenzimmer is neuter:

singular: das Klassenzimmer
dative singular: dem Klassenzimmer → im Klassenzimmer

It’s a compound noun:

die Klasse (class)
das Zimmer (room)

In German compounds, the last part decides the gender.
Since Zimmer is neuter (das Zimmer), the whole compound Klassenzimmer is also neuter → das Klassenzimmer.

Is the word order fixed? Can I say Die Kinder sitzen im Klassenzimmer ruhig?

German word order is somewhat flexible, but there are preferences.

Typical pattern for adverbials:
Verb – Manner – Place – Time
Here:

Verb: sitzen
Manner: ruhig
Place: im Klassenzimmer

So:

Die Kinder sitzen ruhig im Klassenzimmer.
(Very natural: sit – how – where)

Die Kinder sitzen im Klassenzimmer ruhig. is grammatically correct, but sounds a bit marked or less neutral in many contexts. It might put slightly more emphasis on im Klassenzimmer.

You can also move the place phrase to the front:

Im Klassenzimmer sitzen die Kinder ruhig.
(In the classroom, the children are sitting quietly.)

Just remember: in main clauses, the finite verb must stay in 2nd position:

[Im Klassenzimmer] sitzen die Kinder ruhig. ✔

Why are Kinder and Klassenzimmer capitalized, but sitzen and ruhig are not?

In German:

All nouns are capitalized:
- Kinder, Klassenzimmer
Verbs and adjectives/adverbs are not capitalized (except at the beginning of a sentence or in titles):
- sitzen, ruhig

This is a standard rule of German orthography:

Nouns → capital letter
Everything else → lowercase, unless it starts the sentence or is part of a proper noun.

How is ruhig pronounced? Do you say the final g?

Pronunciation (in standard German):

ruhig ≈ [ˈʁuː.ɪç] or [ˈʁuːɪç]

Key points:

r: a uvular sound, made in the back of the throat (different from English r)
u: long oo sound, like in food: ruu
h: after a vowel, mostly silent, just lengthens the vowel
ig at the end:
- often pronounced like -ich: [ɪç] (soft ch as in ich)
- in some regions, you’ll hear it more like -ik [ɪk]

So you often hear something like “roo-ich” or “roo-ig(h)”, but not a hard English g as in big.

Why is it Die Kinder sitzen ruhig im Klassenzimmer and not Die Kinder sind ruhig im Klassenzimmer? Are both correct?

Both are grammatically correct, but they say slightly different things:

Die Kinder sitzen ruhig im Klassenzimmer.
- Focus: They are sitting, and they are doing so quietly/calmly.
- Includes the idea of their posture (sitting).
Die Kinder sind ruhig im Klassenzimmer.
- Focus: They are quiet/calm in the classroom, regardless of whether they’re sitting, standing, etc.
- Describes their state/behavior rather than their posture.

If you want to emphasize that they’re sitting quietly, sitzen ruhig is the better choice.

What is the singular form of Kinder, and how is the plural formed?

The singular is:

das Kind (the child)

The plural is:

die Kinder (the children)

This is an irregular plural:

Vowel changes: i → i (no change here)
Add -er: Kind → Kinder

Other nouns use the same -er plural pattern:

der Mann → die Männer
das Buch → die Bücher

But each noun has its own pattern, so plural forms often have to be memorized.