Зимой дети реже играют на площадке, потому что там холодно.

Зимой is the normal way to say in winter when you mean the season in a general time sense.

Russian often uses the instrumental case with seasons and parts of the day to express when something happens:

• зимой = in winter
• летом = in summer
• осенью = in autumn
• весной = in spring

So Зимой дети... means In winter, children...

Using в зиме would sound wrong here.
в зиму can exist in some contexts, but it usually does not mean the simple seasonal time expression used in this sentence.

Дети means children and it is the irregular plural of ребёнок (child).

This is one of the important irregular noun plurals in Russian:

• ребёнок = child
• дети = children

So you cannot make the plural by regular patterns like ребёнки in standard Russian.

Реже means more rarely, less often, or simply not as often.

It is the comparative form of the adverb редко:

• редко = rarely
• реже = more rarely / less often

In this sentence, дети реже играют means children play less often.

English often uses less often, while Russian commonly uses this one-word comparative adverb.

Good question. Russian comparatives do not always need an explicit than phrase.

Here, реже means something like:

• less often than usual
• less often than in another season
• less often than when it’s warm

The comparison is understood from context, so чем is unnecessary.

If you wanted to say it explicitly, you could say something like:

• Зимой дети играют реже, чем летом.
  In winter, children play less often than in summer.

But in your sentence, the comparison is left implicit.

Играют is the 3rd person plural present tense form of играть (to play).

Why plural? Because the subject is дети (children), which is plural.

Conjugation:

• я играю = I play
• ты играешь = you play
• он/она играет = he/she plays
• мы играем = we play
• вы играете = you play
• они играют = they play

So:

• дети играют = children play

Because this sentence describes a habitual, repeated action: what children generally do in winter.

Russian normally uses the imperfective verb for habits, repeated actions, and general facts:

• играть = to play, to be playing, to play habitually

A perfective form like поиграть would suggest something more like to play for a while or a single completed event, which does not fit as well here.

So дети реже играют means children play less often in general.

Because Russian uses на with many open spaces, surfaces, or activity areas, and a playground is one of them.

• на площадке = on the playground / at the playground

When you talk about location after на, you use the prepositional case:

• площадка → на площадке

This is similar to other expressions like:

• на улице = in the street / outside
• на стадионе = at the stadium
• на рынке = at the market

Using в площадке would be incorrect here.

In this sentence, площадка most naturally means a playground or play area.

The word itself can mean different kinds of platform, site, or area depending on context, but with дети играют на площадке, the natural interpretation is:

• children play on the playground

If you want to be very specific, Russian also has:

• детская площадка = children’s playground

But in many contexts, just площадка is enough.

Because потому что introduces a subordinate clause meaning because.

The sentence has two parts:

• Зимой дети реже играют на площадке
• потому что там холодно

Russian normally separates the main clause and the because clause with a comma.

So the comma is standard and expected here.

Yes. Потому что is one of the most common and neutral ways to say because in Russian.

So:

• ..., потому что там холодно.
• ..., because it is cold there.

It is very common in everyday speech and writing.

Там means there, and here it refers back to на площадке.

So the idea is:

• on the playground
• because there it is cold

Russian often uses там to point back to a place already mentioned, just like English does.

Because холодно is not an adjective here. It is a predicative word used to describe the general environment or condition: it is cold.

Compare:

• холодный день = a cold day
  Here холодный is an adjective describing день.

But:

• На улице холодно. = It is cold outside.
• Там холодно. = It is cold there.

In these sentences, Russian uses холодно, not an adjective agreeing with a noun.

In a way, yes—but Russian does not use a dummy subject like English it.

English says:

• It is cold there.

Russian simply says:

• Там холодно.

This is an impersonal construction. There is no actual subject word equivalent to English it.

That is very normal in Russian with weather and general conditions:

• темно = it is dark
• жарко = it is hot
• холодно = it is cold
• интересно = it is interesting

Yes. Russian word order is flexible, and several versions are possible.

For example:

• Зимой дети реже играют на площадке...
• Зимой дети играют реже на площадке...
• Дети зимой реже играют на площадке...

These all express roughly the same basic meaning, but the position of words can change the focus or emphasis slightly.

Your original sentence is natural and clear. Putting реже before играют emphasizes the frequency idea early: play less often.

Yes, but then the sentence loses the time frame.

Compare:

• Зимой дети реже играют на площадке, потому что там холодно.
  In winter, children play on the playground less often because it is cold there.

• Дети реже играют на площадке, потому что там холодно.
  Children play on the playground less often because it is cold there.

Without Зимой, the sentence is still grammatical, but it no longer specifically says that this happens in winter.