Nećak želi slagalicu, a ne bojanku.

Because they are in the accusative case, which is the usual case for a direct object in Croatian.

The verb željeti / želi means to want, so the thing being wanted goes into the accusative:

• slagalica → slagalicu
• bojanka → bojanku

Both of these nouns are feminine and end in -a in the dictionary form, so in the singular accusative they usually change -a to -u.

So:

• Nećak želi slagalicu = The nephew wants a puzzle
• ...a ne bojanku = ...and not a coloring book

Their base, dictionary forms are:

• slagalica = puzzle / jigsaw puzzle
• bojanka = coloring book

In this sentence, both appear in the accusative singular:

• slagalica → slagalicu
• bojanka → bojanku

This is a very common pattern for feminine nouns ending in -a.

Želi is the 3rd person singular present tense of željeti (to want).

The subject is nećak (nephew), which is he, so Croatian uses the he/she/it form:

• ja želim = I want
• ti želiš = you want
• on/ona želi = he/she wants

So Nećak želi... literally means Nephew wants..., or more naturally in English, The nephew wants...

Here a ne expresses a contrast:

• a = and / while / whereas / but, depending on context
• ne = not

So a ne bojanku means something like:

• and not a coloring book
• rather than a coloring book
• not a coloring book

In this sentence, a is not simply adding information like English and. It is setting up a contrast between two choices:

• slagalicu
• ne bojanku

So the whole sentence contrasts what he wants with what he does not want.

In Croatian, a comma is commonly used before a when it connects two contrasting parts of a sentence.

So:

• Nećak želi slagalicu, a ne bojanku.

This punctuation helps show the contrast clearly. It is very natural and standard here.

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

So nećak, slagalicu, and bojanku appear without articles, and the exact meaning depends on context.

For example:

• Nećak želi slagalicu could mean The nephew wants a puzzle
• In another context, it could also be understood as My nephew wants the puzzle, depending on what has already been mentioned

English requires articles, but Croatian does not.

Yes. Nećak is the subject, and it is in the nominative case.

The structure is:

• Nećak = subject
• želi = verb
• slagalicu = direct object
• a ne bojanku = contrasting object phrase

So Croatian is working here in a very familiar pattern for English speakers:

Subject + Verb + Object

Nećak is pronounced approximately NEH-chak, but with a softer sound than English ch.

The letter ć is one of the sounds English speakers often find tricky. It is softer and more palatal than č.

A rough guide:

• č = a harder ch
• ć = a softer ch, with the tongue a bit more forward

So nećak is not quite the same as a strong English nechak. It is a softer sound.

Also:

• ž in želi sounds like the s in measure or vision

So želi is roughly ZHEH-lee.

Yes. Croatian often omits subject pronouns, and sometimes even a noun subject can be omitted if the context is clear.

For example, if everyone already knows you are talking about the nephew, you could simply say:

• Želi slagalicu, a ne bojanku.

Because the verb form želi already shows he/she wants, the sentence can still be understood from context.

But in your sentence, Nećak is included to make it clear who wants the puzzle.

Yes, Croatian word order is more flexible than English, although the given version is the most neutral and natural.

The sentence:

• Nećak želi slagalicu, a ne bojanku.

is straightforward and standard.

You might change word order for emphasis in some contexts, but learners should treat this version as the normal one.

For example, Croatian often changes word order to emphasize contrast, but that is more advanced. The safest choice is to keep:

• subject + verb + object

In most everyday contexts, yes. Bojanka usually means coloring book, especially for children.

It comes from the idea of coloring (bojati / boja is related to color). So in this sentence, bojanku is the thing the nephew does not want.

Because the sentence is not saying he does not want something in general. It is saying he wants one thing rather than another.

Compare:

• Nećak ne želi bojanku. = The nephew does not want a coloring book.
• Nećak želi slagalicu, a ne bojanku. = The nephew wants a puzzle, not a coloring book.

In your sentence, the negation is focused only on the second noun phrase, not on the whole action of wanting.