Learn Hardcore German: Ich verspreche den Kleinen, dass wir morgen wieder am Bach spielen. - I promise the little ones that we will play by the creek again tomorrow.

Ich (subject, nominative)
verspreche (verb)
den Kleinen (indirect object, dative = the people to whom I promise something)
…, dass wir … spielen. (the content of the promise)

So:
Ich verspreche (wem?) den Kleinen (was?) dass wir morgen wieder am Bach spielen.

Why is Kleinen capitalized here? Is it a noun or an adjective?

Kleinen is originally an adjective (klein = small), but here it’s used as a noun: “the little ones.”

In German, when an adjective is used on its own as a noun (a nominalized adjective), it is written with a capital letter:

die Kleinen – the little ones (children)
die Alten – the old people
der Kleine – the little one (singular, male/child)

So Kleinen is functioning as a noun (meaning “little ones”), which is why it’s capitalized.

Why is it den Kleinen and not die Kleinen?

Because den Kleinen is dative plural, not nominative plural.

die Kleinen = nominative plural (subject):
- Die Kleinen spielen am Bach. – The little ones are playing by the stream.
den Kleinen = dative plural (indirect object):
- Ich verspreche den Kleinen … – I promise to the little ones …

The verb versprechen works like to give in English in terms of structure:
ich verspreche jemandem etwas = I promise someone something.

That “someone” is in the dative, so you need den.

Why is there a comma before dass?

In German, dass introduces a subordinate clause (a that‑clause). Subordinate clauses are separated by a comma from the main clause.

Main clause: Ich verspreche den Kleinen,
Subordinate clause: dass wir morgen wieder am Bach spielen.

The subordinate clause gives the content of the promise:

Ich verspreche den Kleinen – I promise the little ones
dass wir morgen wieder am Bach spielen – that we will play by the stream again tomorrow

So the comma is obligatory in standard written German before dass.

Why is the verb spielen at the end in dass wir morgen wieder am Bach spielen?

Because dass makes this a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end of the clause.

Pattern:
dass + [subject] + [other elements] + [verb at the end]

So:

dass (subordinating conjunction)
wir (subject)
morgen wieder am Bach (time / adverb / place)
spielen (verb at the end)

Compare:

Main clause word order: Wir spielen morgen wieder am Bach.
Subordinate clause: …, dass wir morgen wieder am Bach spielen.

Could I leave out dass and say: Ich verspreche den Kleinen, wir spielen morgen wieder am Bach?

In standard German, you should not leave out dass here. The natural, correct version is:

Ich verspreche den Kleinen, dass wir morgen wieder am Bach spielen.

Without dass, the second part (wir spielen morgen wieder am Bach) sounds like a separate main clause, not the content of the promise. In careful/written German, you need dass to properly connect them.

In some spoken varieties, people might sometimes drop dass in similar constructions, but it can sound colloquial or ungrammatical, depending on the region, and learners should keep the dass.

What is the difference between dass and das here?

In this sentence you must use dass with double s:

dass = subordinating conjunction, like “that” in English:
- Ich verspreche, dass wir morgen wieder am Bach spielen.
das (single s) can be:
- a definite article (neuter): das Haus – the house
- a demonstrative pronoun: das ist gut – that is good
- a relative pronoun: das Haus, das dort steht – the house that stands there

Here we are introducing a that‑clause (content clause), so only dass is correct.

Why is it am Bach and not im Bach or an dem Bach?

am is a contraction of an dem:

an dem Bach → am Bach

an + dative is used for being at/by a vertical boundary or edge or by a body of water (river, stream, lake, sea, etc.):

am Bach – by/at the stream
am See – by the lake
am Meer – by the sea

im Bach is in dem Bach (“in the stream”), which would suggest being in the water (e.g. standing in it).

So:

am Bach spielen – playing by the stream (on the bank, next to it)
im Bach spielen – playing in the stream (in the water)

In this sentence, am Bach = “by the stream.”

Why is verspreche in the present tense, when the action (playing) is in the future?

German often uses the present tense to talk about the future, especially when a time word like morgen (tomorrow) makes the time clear.

Ich verspreche den Kleinen, dass wir morgen wieder am Bach spielen.
= I promise the little ones that we will (shall) play by the stream again tomorrow.

You could theoretically use the future tense with werden:

…, dass wir morgen wieder am Bach spielen werden.

But in everyday German, the present with a future time expression (morgen) is usually preferred and sounds more natural here.

What does wieder do in the sentence, and where can it go?

wieder means “again”.

The basic word order in the subordinate clause is:

dass wir morgen wieder am Bach spielen.
= that we will play by the stream again tomorrow.

This is a good, natural position: wieder comes before the place phrase am Bach and before the verb spielen.

Other possible positions (with slightly different emphasis):

dass wir wieder morgen am Bach spielen. – sounds odd, as if “again tomorrow” is a single chunk; not usual.
dass wir am Bach morgen wieder spielen. – possible, but less neutral; different rhythm/emphasis.

For learners, the safe, neutral option is the one from the sentence:

Subordinate clause: …, dass wir morgen wieder am Bach spielen.
Main clause version: Wir spielen morgen wieder am Bach.

Can I say den Kindern instead of den Kleinen? Does it change the meaning?

Yes, you can say:

Ich verspreche den Kindern, dass wir morgen wieder am Bach spielen.

This is perfectly correct and means:

den Kindern – to the children
den Kleinen – to the little ones (implies they are young/small; more affectionate or descriptive)

den Kleinen emphasizes their smallness / young age, and can sound a bit more affectionate or informal, as adults often refer to small children that way.

So both are grammatical; the nuance is mainly about tone and emphasis, not about structure.