Learn Hardcore German: Erwachsene und Kinder lernen zusammen im Park. - Adults and children study together in the park.

Die Erwachsenen und die Kinder lernen zusammen im Park.
= The adults and the children (those particular ones) are learning together in the park.

So the sentence without articles is a general statement about groups of people, not about specific individuals already mentioned.

What exactly is Erwachsene? Is it a noun or an adjective?

Erwachsene here is a noun meaning “adults” (plural).

It comes from the adjective erwachsen (grown, adult), but it is used as a noun:

der Erwachsene = the adult (male or generic singular, nominative)
die Erwachsene = the adult (female singular, nominative)
die Erwachsenen = the adults (plural, nominative/accusative)

In your sentence, Erwachsene is plural and used without an article, so it simply means “adults”.

Why is lernen used here instead of studieren?

German makes a clear distinction:

lernen = to learn (in general), to study for school, to acquire a skill or knowledge
- Kinder lernen lesen. – Children learn to read.
- Ich lerne Deutsch. – I’m learning German.
studieren = to study at a university, usually in the sense of being enrolled in a course of study / major
- Ich studiere Physik. – I study physics (at university).
- Sie studiert in Berlin. – She is at university in Berlin.

In a park, with adults and children together, this is clearly general “learning,” not university study, so lernen is the natural verb.

Why is it lernen and not lernt?

The verb must agree with the subject in person and number.

The subject is Erwachsene und Kinder – that’s they (3rd person plural).

Conjugation of lernen in the present tense:

ich lerne
du lernst
er/sie/es lernt
wir lernen
ihr lernt
sie lernen

So with a plural subject (adults and children), you must use lernen:

Erwachsene und Kinder lernen zusammen im Park.
= Adults and children learn together in the park.

What case are Erwachsene und Kinder in, and how can I tell?

Erwachsene und Kinder are in the nominative case, because they are the subject of the sentence – the ones doing the action of learning.

A quick way to see it:
Ask “Who is learning?” → Erwachsene und Kinder.

In German, the subject of a normal active sentence is in the nominative.
The object, if there were one, would typically be in accusative or dative, but here we only have the subject and some adverbials (zusammen, im Park).

What does im mean, and why is it used instead of in dem?

im is simply the contracted form of in dem.

in = in
dem = the (dative, masculine/neuter singular)
in dem Park → im Park

This contraction is very common and completely standard in German, especially with location phrases:

im Park = in the park
im Haus = in the house
im Büro = in the office

So im Park literally means “in the (dative) park”.

Why is the preposition in (here as im) followed by the dative (dem Park) and not the accusative?

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

Dative = location (where something is)
Accusative = direction / movement (where something is going)

Your sentence describes a location, not a movement:

They are learning in the park → Wo? (Where?) → Dative

So:

im Park (= in dem Park, dative) → correct for a static location.

If you wanted to express movement into the park, you’d use accusative:

Sie gehen in den Park. – They are going into the park.

Could I move zusammen or im Park to another position? Are there word order rules here?

Yes, you can move them. German word order is flexible, especially for adverbs and prepositional phrases. Some common variants:

Erwachsene und Kinder lernen zusammen im Park. (neutral)
Erwachsene und Kinder lernen im Park zusammen. (slightly more focus on “together” at the end)
Im Park lernen Erwachsene und Kinder zusammen. (focus on the location: as for in the park…)
Zusammen lernen Erwachsene und Kinder im Park. (stronger focus on the togetherness)

All of these are grammatically correct. What must stay is:

The finite verb (lernen) is in 2nd position in a main clause:
- [1st element] + lernen
  - [rest].

Everything else can be rearranged for emphasis or style.

What is the difference between zusammen, miteinander, and gemeinsam here?

All three can express the idea of “together,” but with slightly different nuances:

zusammen
- Very common, neutral “together,” often used for doing something as a group.
- Erwachsene und Kinder lernen zusammen im Park.
miteinander
- Literally “with one another,” can emphasize interaction between the people.
- Erwachsene und Kinder lernen miteinander im Park.
- Slightly stronger sense that they are learning with each other (e.g., cooperating, interacting).
gemeinsam
- Feels a bit more formal or elevated; also “together,” with a sense of shared activity or purpose.
- Erwachsene und Kinder lernen gemeinsam im Park.

All three would be understood; zusammen is the most neutral, everyday choice.

Why is Park capitalized?

In German, all nouns are capitalized, regardless of their position in the sentence.

Erwachsene, Kinder, Park are all nouns, so they all start with a capital letter.

This is a consistent rule and an important visual clue for recognizing nouns in German.

What is the singular and plural of Kind, and what is its gender?

Singular: das Kind (neuter) – the child
Plural: die Kinder – the children

In your sentence, Kinder is the plural form:

Erwachsene und Kinder lernen zusammen im Park.
= Adults and children learn together in the park.

Note: the plural article would be die (die Kinder), but here it’s omitted because the sentence talks about children in general.