Learn Hardcore Russian: Дети смеются и играют на качелях в парке. - Children are laughing and playing on the swings in the park.

The present tense verb ending itself (-ются, -ют, etc.) already shows that the action is happening now, so Russian normally drops the present-tense “to be” (есть) in such sentences.

Does смеются и играют mean “are laughing and are playing” (continuous) or just “laugh and play”? How do you tell?

In Russian, the simple present can cover both meanings:

Дети смеются и играют…
- can be “The children are laughing and playing…” (right now)
- or “Children laugh and play…” (a general statement)

Context decides which one is meant. There is no separate continuous form (like “are laughing”) in Russian; the normal present tense covers both.

Why do we say Дети смеются, and not use a pronoun like Они смеются?

Russian only uses pronouns when needed for clarity or emphasis. Here, дети already tells us who is doing the action.

Дети смеются и играют… = The children are laughing and playing…
Они смеются и играют… = They are laughing and playing… (you’d use this if the children were already mentioned in a previous sentence)

You don’t say both Дети они смеются — that would be wrong or sound very strange in standard Russian.

What case is дети here, and why that form and not детей?

Дети is nominative plural, and it’s the subject of the sentence.

Dictionary form: ребёнок (child), дети (children – irregular plural)
Nominative plural (subject): дети
Genitive plural: детей

You use the nominative for the doer of the action:

Дети смеются. – The children are laughing.
If you needed genitive (for example after some prepositions or quantities), you’d use детей instead, but here it’s the subject, so nominative дети is correct.

Why are the verb endings -ются in смеются and -ют in играют? What do those endings mean?

Both verbs are 3rd person plural, present tense:

смеяться (to laugh) → они смеются
- stem: сме-
- ending: -ются (3rd person plural, reflexive -ся folded into it)
играть (to play) → они играют
- stem: игра-
- ending: -ют (3rd person plural)

So смеются and играют both mean “(they) are laughing / (they) play” and “(they) are playing / (they) play”, and agree with plural дети.

Why is it на качелях and not на качели or something like на качеляхах?

A few points here:

Качели is one of those nouns that are normally only plural (pluralia tantum), like English scissors or trousers.
- Dictionary form: качели (plural)
на качелях uses the prepositional plural:
- plural base: качели
- prepositional plural ending: -ях → качелях
You use на + prepositional to show location:
- Дети играют на качелях. – Children are playing on the swings.

На качели (accusative plural) would typically be used with verbs of motion / direction, e.g.:

Сесть на качели. – To sit down on the swing(s). (movement onto them)

So:

на качелях = on the swings (location, where?)
на качели = onto the swings (direction, where to?)

What case is в парке, and why is в used instead of на?

В парке is prepositional singular:

Dictionary form: парк
Prepositional singular: в парке – in the park

You use в + prepositional for being inside / within a place:

в парке, в доме (in the park, in the house)

You can sometimes see на + prepositional with places too (e.g. на улице – on the street, на стадионе – at the stadium). For парк, the natural choice is в парке, because you’re thought of as being inside the area of the park.

Why is the word order Дети смеются и играют на качелях в парке? Could we say В парке дети смеются и играют на качелях instead?

Yes, you can change the word order in Russian more freely than in English. Both are correct:

Дети смеются и играют на качелях в парке.
В парке дети смеются и играют на качелях.

The main difference is emphasis:

Starting with Дети… emphasizes who is doing the action (the children).
Starting with В парке… emphasizes where this is happening (in the park, as opposed to somewhere else).

Grammar (cases and endings) stays the same, so meaning is clear even when order changes.

Why is качелях plural, but парке singular? Would на парках ever be used?

качели is inherently plural in normal usage, so its forms (including качелях) are also plural.
парк is a regular noun with both singular and plural:
- singular: парк → в парке
- plural: парки → в парках

In this sentence we’re talking about one specific park, so в парке (singular) is correct.

You would only say в парках if you really meant “in parks” in general or in several parks:

Дети часто играют в парках. – Children often play in parks.

Could we say Дети посмеются и поиграют на качелях в парке instead? What would change?

Yes, but the meaning changes because you switch to perfective verbs:

смеются, играют – imperfective, focusing on the process / ongoing action:
- Дети смеются и играют… – They are (now) laughing and playing.
посмеются, поиграют – perfective, focusing on the action as a completed event (for a while, then done):
- Дети посмеются и поиграют на качелях в парке. – The children will laugh and play on the swings in the park (for some time, and then it will be over).

So the original sentence is more like a description of what is happening (or typically happens), not a plan of what will be done and finished.

There’s no “the” or “some” in Дети смеются…. How do we know if it’s “the children” or just “children”?

Russian doesn’t have articles (the, a/an, some). The same Russian sentence can correspond to different English article choices, depending on context:

Дети смеются и играют на качелях в парке.
- The children are laughing and playing on the swings in the park.
- Children are laughing and playing on the swings in the park.

If the children have already been mentioned or are clearly specific, English usually chooses “the children”. If we’re speaking generally, English might use “children” with no article, or “some children”. Russian leaves this to context, not to a special word.