Ispred škole je velika lokva, pa djeca hodaju polako.

Because ispred is a preposition that normally takes the genitive case.

• škola = nominative singular, the basic dictionary form
• škole = genitive singular

So:

• ispred škole = in front of the school

This is very common in Croatian:

• ispred kuće = in front of the house
• ispred zgrade = in front of the building

It is a prepositional phrase.

• ispred = in front of
• škole = of the school / school (in genitive)

Together, ispred škole functions like an adverbial phrase of place: it tells you where something is.

In the sentence, it answers the question:

• Gdje je velika lokva? = Where is the big puddle?

Answer:

• Ispred škole.

Both are possible, but they give slightly different emphasis.

• Ispred škole je velika lokva puts the location first, so it sounds like you are setting the scene: In front of the school, there is a big puddle.
• Velika lokva je ispred škole starts with the subject, so it sounds more like: The big puddle is in front of the school.

Croatian word order is more flexible than English word order. The first version is very natural when introducing a place or situation.

Je is the 3rd person singular form of biti (to be), and Croatian often places short unstressed words like je in the second position of the clause.

So in:

• Ispred škole je velika lokva

the phrase Ispred škole comes first, and je follows early in the sentence.

This is a normal Croatian pattern with clitics (short unstressed words).

Because velika must agree with lokva in gender, number, and case.

• lokva is feminine singular nominative
• so the adjective must also be feminine singular nominative
• that gives velika

Comparison:

• velik pas = a big dog
• velika lokva = a big puddle
• veliko selo = a big village

So velika lokva is just normal adjective-noun agreement.

It is nominative singular.

In this clause:

• Ispred škole je velika lokva

velika lokva is the thing that is there, so it functions as the grammatical subject-like noun phrase of the sentence.

That is why it appears in the nominative:

• lokva = nominative singular

This is a very common learner question. Djeca means children, and although its form may look singular, it refers to a plural group and takes a plural verb.

So:

• djeca hodaju = the children walk / are walking

You should learn djeca as a special plural-type noun meaning a group of children.

Other examples:

• Djeca se igraju. = The children are playing.
• Djeca spavaju. = The children are sleeping.

So hodaju is correct because the meaning is plural.

Both hodati and ići can relate to movement, but they are not the same.

• hodati = to walk
• ići = to go

In this sentence, hodaju polako focuses on the manner of movement: the children are walking slowly, probably because of the puddle.

If you said:

• djeca idu polako

that would mean the children are going slowly, which is possible, but hodaju is more specific and natural when the action is literally walking.

Because polako is an adverb, and adverbs do not agree with nouns the way adjectives do.

Here it modifies the verb:

• hodaju polako = they walk slowly

Compare:

• polak dječak — not correct in standard Croatian for slow boy
• spor dječak = a slow boy
• polako hodaju = they walk slowly

So:

• velika describes the noun lokva
• polako describes the verb hodaju

Here pa means something like:

• so
• therefore
• and so
• sometimes even then, depending on context

In this sentence, it connects the two ideas:

• there is a big puddle in front of the school
• so the children walk slowly

So pa shows a natural consequence.

It is very common in everyday Croatian and often sounds more conversational than a more formal connector.

Not with the same meaning.

• i = and
• ali = but
• pa = so / and so / therefore

In this sentence, pa is best because the second clause follows naturally from the first one.

• Ispred škole je velika lokva, pa djeca hodaju polako. = There is a big puddle in front of the school, so the children walk slowly.

If you used i:

• ..., i djeca hodaju polako = ... and the children walk slowly

This only adds information; it does not clearly show consequence.

If you used ali:

• ..., ali djeca hodaju polako = ... but the children walk slowly

That would suggest contrast, which does not fit the situation.

Because Croatian has no articles like English a/an/the.

Whether something is understood as a school, the school, a big puddle, or the big puddle depends on context.

So:

• škola / škole
• lokva

do not need articles.

English speakers often want to insert the mentally, but in Croatian you simply use the noun form and let the context do the work.

Yes. Both verbs are in the present tense:

• je = is
• hodaju = walk / are walking

Like many languages, Croatian present tense can describe:

• a current situation
• a general present fact
• something happening now

So djeca hodaju polako can mean:

• the children walk slowly or
• the children are walking slowly

The exact English translation depends on context.

Because pa here connects two clauses:

• Ispred škole je velika lokva
• djeca hodaju polako

In standard writing, a comma is normally used before pa when it links clauses like this.

So the comma helps show the structure:

• first situation
• then its consequence

That punctuation is standard and natural here.