Learn Hardcore Polish: Ostatnio dzieci rzadko bawią się na boisku, a częściej siedzą na balkonie z telefonem. - Lately the children rarely play on the field and more often sit on the balcony with a phone.

ostatnio ≈ lately / recently (as a general trend, over a period of time)
It usually refers to something that has been happening repeatedly or habitually in the recent past and often still now.
- Ostatnio dzieci rzadko bawią się na boisku.
  = Lately the children rarely play on the playground. (a current tendency)
niedawno ≈ not long ago / recently (one event or a few specific occasions)
It points more to specific events in the recent past.
- Niedawno dzieci bawiły się na boisku.
  = Not long ago the children played on the playground (once / on some occasion).

In this sentence we’re talking about a general change in habits over recent times, so ostatnio is the natural choice.

Why is there no subject pronoun like one (“they”) before bawią się and siedzą?

In Polish, subject pronouns are usually dropped when the subject is clear from context or from the verb ending.

dzieci rzadko bawią się
The verb ending -ą in bawią tells us it’s 3rd person plural, so we don’t need one.

You could say:

Ostatnio one rzadko bawią się na boisku...

but this sounds like you’re emphasizing they, contrasting them with someone else:

Lately *they rarely play on the pitch (unlike other kids / unlike we expected).*

In a neutral sentence, just dzieci rzadko bawią się is most natural.

What exactly does bawić się mean, and how is it different from grać?

bawić się is a reflexive verb meaning:

to play in the sense of children playing (having fun, amusing themselves),
also to amuse oneself, to have fun more generally.

Examples:

Dzieci bawią się na boisku. – The children are playing on the pitch.
Lubię bawić się z kotem. – I like playing with the cat.

grać means to play in these senses:

to play a game or sport – grać w piłkę, grać w szachy
to play an instrument – grać na gitarze
to act / perform – grać w filmie

So:

Dzieci bawią się na boisku. – Children are just playing, having fun there.
Dzieci grają w piłkę na boisku. – Children are playing football on the pitch (a specific game).

Using grać here would shift the meaning to a particular game rather than general play.

Why does the verb use się: bawią się and not just bawią?

bawić się is a reflexive verb; its dictionary form is bawić się, not just bawić in this sense.

bawić się – to play, to have fun, to amuse oneself.
bawić (without się) – to entertain someone, to amuse someone else.
- Ten klaun bawi dzieci. – This clown entertains the children.

So:

Dzieci bawią się. – The children are playing / having fun.
Rodzice bawią dzieci. – The parents are entertaining the children.

In the given sentence, the children are playing themselves, so bawią się is required.

Why is się placed after bawią and not somewhere else? Can the word order change?

The neutral order is:

dzieci rzadko bawią się na boisku

But się is quite flexible. All of these are grammatically correct, with small differences in emphasis:

Dzieci rzadko się bawią na boisku.
Dzieci się rzadko bawią na boisku.

Some tendencies:

bawią się (verb + się) is the most neutral.
rzadko się bawią emphasizes how rarely they play.
się rzadko bawią puts extra stress on rzadko, making it stand out.

What you can’t do is separate się far away from its verb; it must be close to the verb it belongs to.

What form and case is dzieci, and why doesn’t it look like a regular plural?

dzieci is:

the nominative plural of dziecko (child),
and also used for genitive plural, dative plural, accusative plural, locative plural, instrumental plural — it’s an irregular word.

Key forms:

singular:
- dziecko (nom/acc) – child
plural:
- dzieci – children (most cases, including nominative)

In this sentence, dzieci is the subject, so it’s in nominative plural:

(Co?) Dzieci rzadko bawią się... – Children rarely play...

Why do we say na boisku and na balkonie? Which case is used and why?

Here na means “on / at (a location)”, and with that meaning it normally takes the locative case.

boisko (neuter noun, “pitch / playing field”)
- locative singular: na boisku
balkon (masculine noun, “balcony”)
- locative singular: na balkonie

So:

bawić się na boisku – to play on the pitch / playground
siedzieć na balkonie – to sit on the balcony

Compare:

na + locative = location: na balkonie, na stole, na dworcu
na + accusative = direction onto something:
- Idę na boisko. – I’m going to the pitch.
- Wychodzi na balkon. – She goes out onto the balcony.

What is the role of a in ..., a częściej siedzą...? Why not i or ale?

Polish has several conjunctions often translated as “and / but”, but they each carry nuance.

i – simple “and”, just adding information, no contrast.
ale – clear “but”, strong contrast or opposition.
a – something between “and” and “but”:
- links two clauses about the same subject
- often implies contrast, comparison, or different aspect of the same thing.

In this sentence:

Ostatnio dzieci rzadko bawią się na boisku, a częściej siedzą na balkonie z telefonem.

a suggests a contrast in habits:

they rarely do X, whereas they more often do Y.

If you used:

..., i częściej siedzą... – this would sound less contrastive, more like just adding another activity.
..., ale częściej siedzą... – this would feel a bit heavier / stronger, more like a clear “but instead they…”.

a is the most natural here to show a soft contrast between two tendencies.

How do rzadko and częściej work grammatically? Why not często in both parts?

Both are adverbs of frequency, but częściej is the comparative form.

rzadko – rarely, seldom (positive degree)
często – often (positive degree)
częściej – more often (comparative of często)
rzadziej – more rarely (comparative of rzadko)

In the sentence:

rzadko bawią się na boisku – they rarely play there
częściej siedzą na balkonie – they more often sit on the balcony

The structure is:

rzadko (low frequency of activity A)
a częściej (higher frequency of activity B in comparison)

You could say:

Rzadko bawią się na boisku, a często siedzą na balkonie.

That would mean:

They rarely do A, and often do B (no explicit comparison with “more”).

Using częściej emphasizes the comparison: B happens more often (than A).

Why is it z telefonem and not something like na telefonie or przy telefonie?

z + instrumental case (z telefonem) generally means:

“with (in possession of / accompanied by) a phone”
Here it suggests they are sitting with a phone in hand / using a phone.

Case:

telefon (masculine noun)
- instrumental singular: z telefonem

Other options have different meanings:

na telefonie (locative) – literally “on the phone”, but in Polish this usually refers to on the device physically (e.g. data stored there) or speaking by phone in some contexts, not to “sitting with a phone”.
przy telefonie (locative) – “by / near the phone”, e.g. standing next to where the phone is.

So to express “sitting on the balcony with a phone (in their hands)” the natural phrase is:

siedzą na balkonie z telefonem.

Why are bawią and siedzą in the present tense, when English might say “have been playing / have been sitting”?

Polish usually uses the simple present tense with time adverbs like ostatnio to express meanings that in English often use “have been doing”.

Ostatnio dzieci rzadko bawią się na boisku...
can be translated as:
- Lately the children *rarely play on the pitch...*
  or more naturally:
- Lately the children *have been playing on the pitch less often...*

There is no separate present perfect tense in Polish. Instead, Poles use:

present tense
- adverbs like ostatnio, często, rzadko, zawsze
  to express ongoing or habitual actions in the recent past up to now.

So bawią się and siedzą are straightforward present forms:

(one) bawią się – they play / are playing
(one) siedzą – they sit / are sitting

The nuance of “lately / have been doing” comes from ostatnio, not from a special tense.