Learn Hardcore Russian: В парке стоит детский аттракцион.

Accusative (в парк) → motion into a place:
Я иду в парк. – I am going to the park.
Prepositional (в парке) → being in a place:
Я в парке. – I am in the park.

In В парке стоит детский аттракцион, the ride is simply located in the park, not moving there, so в парке (prepositional) is correct, not в парк.

Why does парке end in -е?

Парк is a masculine noun. Its singular forms include:

Nominative: парк (used for the subject)
Prepositional: в парке, о парке (used after в / на for location, and after о for “about”)

The prepositional singular ending for most masculine and neuter nouns is -е, so:

парк → в парке
город → в городе
лес → в лесу (this one is irregular)

So в парке is just the regular prepositional form “in the park”.

Why is the verb стоит used? Literally it means “stands”, but here it means “there is”, right?

Yes. Literally, стоит is “stands”, from стоять (to stand), but Russian very often uses стоять for objects that are standing somewhere as permanent or semi-permanent items:

В комнате стоит стол. – There is a table in the room.
У дома стоит машина. – There is a car by the house.

In English we normally say “there is / there are”, but in Russian you often choose a more specific verb:

лежит (lies) for objects lying horizontally: На столе лежит книга.
висит (hangs) for hanging objects: На стене висит картина.
стоит (stands) for upright or installed objects: В парке стоит детский аттракцион.

So стоит here combines “is located” with the sense of “stands there as an object”.

Could I say находится instead of стоит?

Yes, you can say:

В парке находится детский аттракцион.

Находится is a neutral, formal-sounding verb meaning “is located / is found”. It does not add the physical nuance of “standing” that стоит has.

Differences:

стоит – natural, everyday, slightly more visual (you imagine the ride standing there).
находится – more neutral, often used in texts, signs, descriptions:
Музей находится в центре города.

Both are grammatically correct here; the original just sounds more colloquial and vivid.

Why is there no word for “a” or “the” before детский аттракцион?

Russian has no articles (no words for a/an or the). The phrase детский аттракцион can mean:

a children’s ride
the children’s ride
just children’s ride (in a general sense)

Which one is meant depends on context, not on a separate word.
In isolation, В парке стоит детский аттракцион is most naturally translated as:

There is a children’s ride in the park.

But in a context where both speaker and listener already know which ride is meant, it could be the children’s ride.

Is детский аттракцион the subject of the sentence, even though it comes after the verb?

Yes. Grammatically, детский аттракцион is the subject:

It is in nominative case (no ending change from the dictionary form аттракцион).
The verb стоит is 3rd person singular, matching аттракцион (masculine singular noun).

Russian word order is more flexible than in English. Compare:

Детский аттракцион стоит в парке. – neutral word order.
В парке стоит детский аттракцион. – emphasizes where it is (in the park).

So even though the subject comes at the end, the grammar (case and verb agreement) clearly shows it is the subject.

What exactly does детский mean here? Is it “childish” or “for children”?

Детский is an adjective formed from дети (children). Its main meaning is “for children / relating to children”:

детский сад – kindergarten (literally: children’s garden)
детская одежда – children’s clothes
детский аттракцион – a ride for children

It can also mean “childish” in a more figurative way:

детский поступок – a childish act

In this sentence, детский аттракцион clearly means “a ride intended for children”, not “a childish ride” in a negative sense.

Why is it детский аттракцион and not something like детей аттракцион to show possession like “children’s ride”?

English often uses a possessive noun (children’s) to modify another noun. Russian more often uses an adjective formed from the noun:

ребёнок → детский (child → children’s / for children)
Россия → российский (Russia → Russian, relating to Russia)
школа → школьный (school → school-related)

So instead of a genitive phrase like аттракцион детей, Russian uses the adjective:

детский аттракцион – a children’s ride (for children)

A phrase like аттракцион детей would sound unnatural or would have a different, forced meaning (e.g., “the attraction belonging to some specific children” in a very strange context).

Can the verb be omitted, like in В парке детский аттракцион?

Yes, in Russian the present-tense “to be” is often omitted:

Я студент. – I am a student. (no verb am)
Он учитель. – He is a teacher.

With existential sentences (saying that something exists somewhere), the verb can also be omitted in very simple, colloquial or descriptive style:

В парке детский аттракцион.

This is understandable and can appear in speech or in notes/captions, but:

В парке стоит детский аттракцион.

sounds more natural and complete in neutral, standard speech. The explicit verb also adds the nuance that the object is standing there.

How would I say “There are children’s rides in the park” (plural)?

Singular (original):

В парке стоит детский аттракцион. – There is a children’s ride in the park.

Plural:

В парке стоят детские аттракционы. – There are children’s rides in the park.

Changes:

Noun plural: аттракцион → аттракционы
Adjective plural: детский → детские
Verb plural: стоит → стоят (3rd person plural of стоять)

The prepositional phrase в парке stays the same, because it already is in the correct case.