Djeca žele krafne poslije ručka.

Yes. Djeca means children, and it is the irregular plural related to dijete (child).

This is one of those forms you usually just learn as a pair:

• dijete = child
• djeca = children

So even though djeca does not look like the singular, it is the normal word for children.

Because djeca is plural in meaning, so the verb also appears in the plural.

• želi = he/she/it wants
• žele = they want

So:

• Dijete želi = The child wants
• Djeca žele = The children want

Here, žele is the 3rd person plural present-tense form of željeti (to want).

Krafne is the plural form of krafna (doughnut / donut).

In this sentence, it is the direct object of žele, so it is in the accusative plural. For this noun, the accusative plural looks the same as the nominative plural:

• krafna = donut
• krafne = donuts

So Djeca žele krafne means The children want donuts.

Because poslije (after) requires the following noun to be in the genitive case.

The dictionary form is:

• ručak = lunch

But after poslije, it changes to genitive:

• poslije ručka = after lunch

This is a very common pattern in Croatian:

• poslije škole = after school
• poslije posla = after work
• poslije ručka = after lunch

It is genitive singular.

The noun ručak is singular, and the preposition poslije asks for the genitive, so:

• nominative: ručak
• genitive: ručka

That is why the sentence has poslije ručka.

Croatian does not have articles like English the and a/an.

So Djeca žele krafne poslije ručka can mean things like:

• The children want donuts after lunch
• Children want donuts after lunch
• The children want the donuts after lunch

The exact meaning depends on context. Croatian usually leaves this unstated unless something else in the sentence makes it clear.

Not completely. Croatian word order is more flexible than English word order.

The sentence as given, Djeca žele krafne poslije ručka, is a normal, neutral order.

But you could also say:

• Poslije ručka djeca žele krafne.
• Krafne djeca žele poslije ručka.

These versions shift emphasis a little, but the basic meaning stays the same. English usually cannot move words around this freely.

Yes. Nakon ručka also means after lunch.

So both are correct:

• poslije ručka
• nakon ručka

In many situations they are interchangeable. Nakon can sound a bit more formal or neutral, while poslije is very common in everyday speech.

The dictionary forms are:

• djeca = children
  related singular: dijete = child
• krafna = donut
• ručak = lunch

In the sentence, krafne and ručka are changed forms:

• krafne from krafna
• ručka from ručak

That is very normal in Croatian, because nouns change form depending on number and case.