Djeca su dobila po jednu mrkvu da nahrane koze.

Djeca is a special word. It means children, and it is the normal plural counterpart of dijete (child).

So:

• dijete = child
• djeca = children

Even though djeca ends in -a, it does not mean one child. Croatian has a few nouns like this that have unusual plural forms.

You can tell it is plural here because the sentence uses su, the plural form of to be in the past tense.

Croatian often forms the past tense with:

• a form of biti (to be)
• plus a past participle

Here:

• su = they are / they have as an auxiliary
• dobila = got / received

Together, su dobila means got / received.

So the structure is similar to a compound past tense:

• Djeca su dobila = The children got / received

Because djeca takes a special kind of plural agreement.

With many plural human subjects, you might expect:

• dobili for masculine/mixed groups
• dobile for feminine groups

But djeca behaves differently. The normal standard form is:

• Djeca su dobila

So this is something worth learning as a set pattern:

• Djeca su došla
• Djeca su jela
• Djeca su dobila

If the subject were dječaci (boys), you would say dobili.
If it were djevojčice (girls), you would say dobile.

Here po means each or apiece.

So:

• po jednu mrkvu = one carrot each

This is a very common Croatian pattern for distributive meaning:

• Dobili su po jedan dar. = They got one present each.
• Učenici su dobili po dvije knjige. = The students got two books each.

So in your sentence, the idea is not just a carrot, but one carrot for each child.

Because this noun phrase is in the accusative, not the nominative.

The children received something, so mrkvu is the direct object.

Base form:

• jedna mrkva = one carrot

Object form:

• jednu mrkvu = one carrot

Both words change because they must match in gender, number, and case:

• jedna → jednu
• mrkva → mrkvu

Since mrkva is feminine singular, the accusative form is mrkvu, and the numeral/adjective must match it: jednu.

Not in this sentence.

Here da introduces a purpose clause, so it means something like:

• so that
• in order to

So:

• da nahrane koze = so that they can feed the goats / in order to feed the goats

Croatian uses da in several different ways, and one of the most common is this purpose meaning.

After da, Croatian normally uses a present-tense verb form, not an infinitive.

So instead of something shaped like English to feed, Croatian says:

• da nahrane

Here nahrane is the 3rd person plural present form of nahraniti.

Why plural? Because the understood subject is still djeca.

So the logic is:

• Djeca su dobila... da nahrane koze.
• The children got ... so that they feed the goats.

Croatian usually does not repeat the subject pronoun if it is already clear.

This is mainly about aspect.

• hraniti = imperfective, more like to feed / be feeding / feed regularly
• nahraniti = perfective, more like to feed successfully / feed once / give food to

In this sentence, the idea is a single completed action: the children got carrots in order to feed the goats. Because of that, nahraniti is very natural.

So:

• da nahrane koze suggests one feeding event
• da hrane koze would sound more like ongoing or habitual feeding

Both verbs relate to feeding, but the aspect changes the nuance.

Because Croatian often drops subject pronouns when the verb already makes the subject clear.

In English, you need:

• so that they feed the goats

In Croatian, the verb form itself already tells you it is 3rd person plural, so oni is unnecessary:

• da nahrane koze

If you added oni, it would usually be for extra emphasis or contrast.

Because the verb nahraniti takes a direct object in the accusative.

You feed someone/something:

• nahraniti koga? što? = to feed whom? what?

So:

• koze is accusative plural here

This may be confusing because in English we often think of feed the goats as something like giving food to the goats. But Croatian treats goats as the direct object of nahraniti.

Also, for many feminine plural nouns, the nominative plural and accusative plural look the same:

• koze = goats
• vidim koze = I see goats
• nahrane koze = they feed the goats

The word order is fairly flexible, but this version is the most neutral and natural.

• Djeca su dobila po jednu mrkvu da nahrane koze.

A few useful points:

• su is a clitic, so it usually comes near the second position in the clause
• the basic order here is very natural for everyday Croatian
• changing the order usually changes emphasis, not the core meaning

For example, moving po jednu mrkvu earlier could emphasize one carrot each more strongly.

So the sentence is not completely fixed, but the given order is the normal unmarked one.