Djeca skupljaju školjke pokraj stijena dok se mi sunčamo na ležaljkama.

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

So:

• djeca can mean children or the children
• školjke can mean shells or the shells
• stijena can mean rocks or the rocks
• ležaljkama can mean deck chairs / loungers or the deck chairs / loungers

Whether something is definite or indefinite is usually understood from context.

Because djeca means children, and it takes plural agreement.

A learner may notice that djeca does not look like a typical plural form, but it is the normal plural of dijete (child). In standard Croatian, it goes with:

• plural verbs: Djeca skupljaju
• plural adjectives: mala djeca

So skupljaju is plural because the subject is djeca.

Školjke is the direct object of skupljaju, so it is in the accusative plural.

Base form:

• školjka = shell

Plural:

• nominative plural: školjke
• accusative plural: školjke

For many feminine nouns in Croatian, the nominative plural and accusative plural look the same, so here školjke is accusative plural because it is what the children are collecting.

Because pokraj is a preposition that takes the genitive case.

Base noun:

• stijena = rock, cliff

Forms:

• singular genitive: stijene
• plural genitive: stijena

So:

• pokraj stijene = beside a rock / the rock
• pokraj stijena = beside rocks / the rocks

In your sentence, the meaning is plural, so Croatian uses stijena as the genitive plural.

Pokraj means beside, next to, or by.

It is very similar to:

• pored
• sometimes kraj

So pokraj stijena means something like:

• beside the rocks
• next to the rocks
• by the rocks

It is a normal and natural word, a little more formal or literary than pored in some contexts, but still very common.

Here dok means while.

It connects two actions that happen at the same time:

• Djeca skupljaju školjke
• mi se sunčamo na ležaljkama

So the structure is:

• X dok Y = X while Y

Be aware that dok can also mean until in other sentences, but in this sentence it clearly means while because both actions are ongoing at the same time.

Because the verb is sunčati se, which means to sunbathe.

The little word se is a reflexive clitic. In many Croatian verbs, it is just part of the verb expression and must be learned together with the verb.

So:

• sunčati se = to sunbathe
• sunčamo se = we sunbathe / we are sunbathing

Without se, sunčati usually means something more like to expose someone/something to the sun, not simply to sunbathe.

Because Croatian often drops subject pronouns, but speakers can include them for emphasis, contrast, or clarity.

So:

• sunčamo se already means we are sunbathing
• mi se sunčamo adds emphasis to we

In this sentence, mi helps create a contrast:

• Djeca are collecting shells
• mi are sunbathing

If you removed mi, the sentence would still be correct:

• Djeca skupljaju školjke pokraj stijena dok se sunčamo na ležaljkama.

Because na here expresses location, and with location it takes the locative case.

Base noun:

• ležaljka = deck chair, sun lounger

Plural locative:

• ležaljkama

So:

• na ležaljkama = on the deck chairs / on the loungers

This is different from motion toward a place. For example:

• Sjedamo na ležaljke = We are sitting down onto the loungers
  
  • motion, so accusative
• Sjedimo na ležaljkama = We are sitting on the loungers
  
  • location, so locative

In your sentence, the action happens on the loungers, so na ležaljkama is locative plural.

Croatian does not have a separate grammatical tense that works exactly like the English present continuous.

Instead, it often uses the present tense of an imperfective verb to express an action that is ongoing right now.

Here:

• skupljaju = they collect / they are collecting
• sunčamo se = we sunbathe / we are sunbathing

Because of the context and the imperfective verbs, English naturally translates them with are collecting and are sunbathing.

Not completely. Croatian word order is fairly flexible, although some orders sound more neutral than others.

Your sentence has a very natural neutral order:

• Djeca skupljaju školjke pokraj stijena dok se mi sunčamo na ležaljkama.

You could also say:

• Dok se mi sunčamo na ležaljkama, djeca skupljaju školjke pokraj stijena.

That still means the same thing.

One important point: se usually has to stay in an early position in its clause, not just anywhere. So learners should not treat word order as completely free. The sentence can move around, but little clitic words like se follow special placement rules.