Learn Hardcore German: Am Bach spielen die Kinder mit Steinen, während die Alten leise Geschichten erzählen. - By the creek the children play with stones while the elderly quietly tell stories.

German main clauses usually have the finite verb in 2nd position (the V2 rule).
The element in 1st position can be many things: the subject, an adverb, a prepositional phrase, etc.

Die Kinder spielen am Bach.
- 1st position: Die Kinder (subject)
- 2nd position: spielen (verb)
Am Bach spielen die Kinder.
- 1st position: Am Bach (prepositional phrase)
- 2nd position: spielen (verb)
- Subject die Kinder comes after the verb.

Starting with Am Bach makes the location more prominent: At the stream is where the children are playing. It sounds a bit more descriptive or literary.

What exactly does am mean in Am Bach?

Am is a contraction of an + dem:

an = at / by / on (vertical surfaces, borders, bodies of water, etc.)
dem = dative singular of the definite article der (masculine)

Bach is masculine (der Bach), and with a stationary location we use dative:

an + dem Bach → am Bach = by/at the stream

So Am Bach literally means “at the stream” in the dative case.

Why is it mit Steinen and not mit Steine?

The preposition mit in German always takes the dative case.

The noun is Stein (stone).
Nominative/accusative plural: Steine
Dative plural: Steinen (German typically adds -n to the dative plural, if there isn’t one already.)

So, because of mit (dative) and plural, we get:

mit + Steinen = with stones (dative plural)
mit Steine would be grammatically wrong.

What is going on with die Alten? Why is an adjective used like a noun?

Die Alten is a nominalized adjective: an adjective used as a noun, which is very common in German.

Base adjective: alt (old)
As a noun: der Alte (the old man), die Alte (the old woman), die Alten (the old people / the elderly)

Key points:

The adjective is capitalized when used as a noun: Alten.
It takes normal adjective endings according to case, gender, and number.
In this sentence, die Alten is nominative plural = the old people / the elders / the elderly.

So während die Alten … erzählen = while the old people tell stories.

Why is there a comma before während, and why is erzählen at the end?

Während is a subordinating conjunction (like weil, dass, wenn).

In German, subordinating conjunctions send the conjugated verb to the end of the clause.
Subordinate clauses are separated from the main clause by a comma.

Structure of the sentence:

Main clause: Am Bach spielen die Kinder mit Steinen,
Subordinate clause: während die Alten leise Geschichten erzählen.

In the subordinate clause während die Alten leise Geschichten erzählen:

während is first
Subject die Alten follows
Other elements leise Geschichten
Verb erzählen comes at the end.

That’s why you get erzählen at the very end of the clause.

Why is it spielen and not spielt in Am Bach spielen die Kinder?

The verb has to agree with the subject in person and number.

Subject: die Kinder = 3rd person plural
The present tense of spielen:
- ich spiele
- du spielst
- er/sie/es spielt
- wir / ihr / sie spielen

So, for die Kinder (they), you must use spielen.

The inversion (verb before subject) in Am Bach spielen die Kinder doesn’t change the agreement:
the verb still matches die Kinder.

Why is the present tense used? In English we might say “are playing” and “are telling”.

German Präsens (simple present) covers both:

English simple present: they play
English present progressive: they are playing

So:

Am Bach spielen die Kinder … can mean “The children play at the stream …” or “The children are playing at the stream …” depending on context.
Likewise, die Alten … erzählen can be “the old people tell” or “are telling”.

German does not need a separate progressive form to express an ongoing action.

What is the function of leise in leise Geschichten erzählen? Is it an adjective or an adverb?

In leise Geschichten erzählen, leise can be understood in two ways:

As an adjective:
- leise Geschichten = quiet/soft stories
  (stories that are themselves gentle/soft in tone)
As an adverb (more likely in actual usage):
- leise erzählen = to tell quietly / softly
  (describes how they tell the stories)

German is often ambiguous here, because many adjectives and adverbs have the same form.
A more strictly adverbial version would be erzählen leise Geschichten or erzählen Geschichten leise, but leise Geschichten erzählen is a natural and idiomatic bundle meaning roughly “quietly tell stories”.

Why is it Geschichten erzählen and not something like von Geschichten erzählen?

Geschichten erzählen is a very common collocation in German and means “to tell stories”:

eine Geschichte erzählen = to tell a story
Geschichten erzählen = to tell stories

When you say von etwas erzählen, it’s more like “talk about something / tell about something”, e.g.:

Er erzählt von seiner Kindheit. = He talks about his childhood.

In the sentence:

… die Alten leise Geschichten erzählen.
→ the old people tell stories quietly.

No von is needed; Geschichten is the direct object of erzählen.

Why is it der Bach and not der Fluss? What is the difference?

Both refer to flowing water, but they differ in size and usage:

der Bach = a stream, brook, or creek — usually smaller, shallower.
der Fluss = a river — generally larger and more significant.

So am Bach suggests a small, perhaps rural or idyllic stream where children might play with stones.
If you said am Fluss, you’d picture a larger river.

Why are die Kinder and die Alten both with die, even though one refers to children and the other to old people?

Die can be:

feminine singular definite article (die Frau)
plural definite article for all genders (die Kinder, die Männer, die Frauen)

Here, both die Kinder and die Alten are plural:

das Kind → die Kinder (plural)
der Alte / die Alte → die Alten (plural)

So:

die Kinder = the children (plural)
die Alten = the old people / the elderly (plural)

Same article die because they’re both plural, not because of gender.

Could the word order in the subordinate clause be während die Alten Geschichten leise erzählen? Is that still correct?

Yes, während die Alten Geschichten leise erzählen is also grammatically correct.

In subordinate clauses, everything before the final verb can be rearranged fairly freely to change nuance or rhythm:

während die Alten leise Geschichten erzählen
während die Alten Geschichten leise erzählen

Both mean essentially “while the old people quietly tell stories”.
The first might slightly highlight “quiet stories” as a phrase; the second slightly highlights the quiet manner of telling, but in practice the difference is very subtle.