W lutym szkoły mają ferie, więc w pociągu jest więcej rodzin z dziećmi.

Because after w meaning in for time expressions, Polish usually uses the locative case.

• luty = February
• w lutym = in February

So the noun changes form:

• styczeń → w styczniu
• luty → w lutym
• marzec → w marcu

This is very common with months in Polish.

Ferie means school holidays/break, especially the break from school in winter or sometimes between terms, depending on context.

In this sentence, W lutym szkoły mają ferie most naturally means that schools are on their winter holiday break, so families travel more.

A useful contrast:

• ferie = school break, especially winter break
• wakacje = summer holidays / summer vacation

So ferie is not just any holiday; it is strongly connected with schools and students.

That is a normal Polish way to express that schools are on break.

Polish often uses mieć (to have) in places where English prefers be on:

• Szkoły mają ferie = schools are on holiday / schools have a break
• Mam przerwę = I have a break
• Mamy wakacje = We’re on vacation / It’s vacation time for us

So although it sounds a bit different from English, it is idiomatic Polish.

Because ferie is a plural-only noun in normal usage. In grammar terms, it is similar to words that are normally used only in the plural.

So you say:

• ferie są
• mam ferie
• szkoły mają ferie

You generally do not use a singular form in everyday Polish for this meaning.

This is similar to how some English nouns are typically plural in form, though the exact category does not match perfectly across the two languages.

Więc means so, therefore, or thus.

In this sentence:

• W lutym szkoły mają ferie, więc w pociągu jest więcej rodzin z dziećmi.
• In February schools have a break, so there are more families with children on the train.

It often connects cause and result.

Its position is fairly flexible, but this placement is very natural. In speech, więc often introduces the consequence of what was just said.

Again, because w here means in, so it requires the locative case.

• pociąg = train
• w pociągu = on the train / in the train

So the noun changes:

• pociąg → w pociągu

Even though English often says on the train, Polish uses w pociągu literally in the train.

This is a very common pattern in Polish.

When you use expressions like więcej (more), mniej (less/fewer), dużo (a lot of), mało (few/little), Polish often uses:

• jest
  • quantity expression + genitive
• było
  • quantity expression + genitive
• będzie
  • quantity expression + genitive

So:

• jest więcej rodzin = there are more families

Why jest and not są?
Because the construction is centered around the quantity expression więcej, and Polish commonly uses singular neuter-style existential phrasing here.

Compare:

• W pociągu są rodziny. = There are families on the train.
• W pociągu jest więcej rodzin. = There are more families on the train.

Both are correct, but they are different structures.

Because więcej requires the genitive case.

• base form: rodzina = family
• nominative plural: rodziny
• genitive plural: rodzin

Since the sentence says więcej rodzin (more families), you need the genitive plural form rodzin.

This is one of the most important patterns to learn:

• dużo ludzi = a lot of people
• mało czasu = little time
• więcej rodzin = more families
• mniej problemów = fewer problems

Because z meaning with requires the instrumental case.

• dzieci = children
• instrumental plural: dziećmi
• z dziećmi = with children

So:

• rodziny z dziećmi = families with children

Be careful: z has more than one meaning in Polish.

• z
  • instrumental = with
• z
  • genitive can mean from / off

Here it clearly means with, so instrumental is used.

Yes, it is irregular, and that is normal.

The noun dziecko (child) has unusual plural forms:

• singular: dziecko
• plural: dzieci

Then in other plural cases:

• genitive plural: dzieci
• dative plural: dzieciom
• instrumental plural: dziećmi
• locative plural: dzieciach

So z dziećmi is something you simply need to learn as a set phrase. It is very common.

Yes, grammatically you could say that, but it changes the nuance.

• Szkoły mają ferie = schools are on holiday / it is school break
• Szkoły są zamknięte = schools are closed

The first one focuses on the holiday period.
The second one focuses more on the physical state of being closed.

In the given sentence, mają ferie is better because the point is that schoolchildren are off school, which explains why more families are traveling.

Not completely. Polish word order is more flexible than English, because case endings show grammatical relationships.

The given sentence is very natural:

• W lutym szkoły mają ferie, więc w pociągu jest więcej rodzin z dziećmi.

But some parts could move for emphasis, for example:

• W lutym szkoły mają ferie, więc więcej rodzin z dziećmi jest w pociągu.
• Więc w lutym w pociągu jest więcej rodzin z dziećmi.

These alternatives may sound more marked or less neutral depending on context. The original version is smooth and standard.

Here z dziećmi describes rodzin.

So the structure is:

• więcej [rodzin z dziećmi]
• more [families with children]

It does not mean that something is happening with children in a broader sentence-level sense. It specifically tells you which families: families who have children with them.

Yes. This is just a difference between English and Polish usage.

English often says:

• on the train
• on the bus
• on the plane

Polish usually says:

• w pociągu = on/in the train
• w autobusie = on/in the bus
• w samolocie = on/in the plane

So you should translate by meaning, not word-for-word. In this sentence, w pociągu is the normal Polish way to say on the train.