Djeca su gledala žabu koja je bila u travi.

Because žabu is the accusative singular form of žaba.

Here, žaba is the direct object of gledala (watched / were watching), and direct objects after this verb normally go in the accusative:

• žaba = nominative, the basic dictionary form
• žabu = accusative, used here as the object

So:

• Djeca su gledala žabu. = The children were watching a frog.

Croatian past tense is usually made with:

• a present-tense form of biti (to be)
• plus the l-participle

So:

• su = are/have-type auxiliary form for they
• gledala = past participle of gledati

Together, su gledala forms the past tense: were watching / watched.

Without su, the sentence would not be standard Croatian past tense.

This is because the subject is djeca (children), which behaves a bit irregularly in Croatian.

Although it refers to multiple children, djeca often takes a neuter plural agreement pattern in forms like the past participle. That is why you get:

• Djeca su gledala.

not:

• Djeca su gledali.

This is something learners usually just have to get used to as a special pattern with djeca.

Koja is a relative pronoun, meaning who/which/that depending on the sentence.

It refers back to žabu and introduces more information about it:

• žabu koja je bila u travi
• the frog that was in the grass

So koja connects the noun žabu with the relative clause je bila u travi.

Because the case of koja is determined by its job inside the relative clause, not by the case of the noun it refers to.

In:

• žabu koja je bila u travi

the pronoun koja is the subject of je bila, so it must be nominative.

That is a very important point:

• žabu is accusative because it is the object of gledala
• koja is nominative because it is the subject of je bila

Even though both refer to the same frog, they have different grammatical roles.

For the same reason as su gledala in the main clause: Croatian past tense needs an auxiliary plus a participle.

Here:

• je = auxiliary, is/has form for she/it
• bila = past participle of biti in feminine singular

It is feminine singular because koja refers to žaba, and žaba is a feminine noun.

So:

• koja je bila = which was / that was

Because u can take different cases depending on meaning.

Here it means location: the frog was in the grass, so Croatian uses the locative:

• trava = basic form
• u travi = in the grass

If there were motion into the grass, Croatian would use the accusative:

• u travu = into the grass

So:

• bila u travi = was in the grass
• skočila u travu = jumped into the grass

Because u travi suggests being in/among the grass, surrounded by it.

• u travi = in the grass
• na travi = on the grass

So if the frog is hidden among blades of grass, u travi is the natural choice.

No. In this sentence, it clearly refers to žabu.

Why?

Because koja is feminine singular, and that matches žaba. It does not match djeca.

So the structure is:

• Djeca su gledala [žabu koja je bila u travi].

The relative clause describes the frog, not the children.

Because su is a clitic, and Croatian clitics usually go in the second position in the clause.

So the natural order is:

• Djeca su gledala žabu...

not:

• Djeca gledala su žabu...

This second-position rule is very common in Croatian and affects short forms like sam, si, je, smo, ste, su.

Here are the main forms:

• djeca → plural of dijete = child
• su → form of biti = to be
• gledala → from gledati = to watch, look at
• žabu → from žaba = frog
• koja → from koji = which, who, that
• je bila → from biti = to be
• travi → from trava = grass

This is useful because Croatian words often change form depending on case, number, and gender.

It can often correspond to either in English, depending on context.

The verb gledati is imperfective, so it usually suggests an ongoing or repeated action rather than a single completed one. In many contexts, that fits English were watching very well.

So this sentence can naturally be understood as something like:

• The children were watching the frog that was in the grass.

But in some contexts English might also translate it simply as watched.

Yes. Djeca is one of the most important irregular nouns for learners.

The singular is:

• dijete = child

But the plural is not a regular form like you might expect. Instead, it is:

• djeca = children

It also shows special agreement behavior, which is why you see:

• Djeca su gledala

This is a very common word, so it is worth memorizing early.