Djeca gledaju veliki mjehurić u parku.

Here is a word-by-word breakdown:

• Djeca = children
• gledaju = watch / are watching
• veliki = big
• mjehurić = bubble
• u = in
• parku = park, here in the form meaning in the park

So the structure is:

• Djeca = subject
• gledaju = verb
• veliki mjehurić = direct object
• u parku = location

Djeca means children. In English, that is clearly plural, and in Croatian it also behaves as plural for agreement in sentences like this one.

That is why the verb is gledaju and not gleda:

• Dijete gleda = The child is watching
• Djeca gledaju = The children are watching

So for a beginner, the important thing is: djeca means children and takes a plural verb.

Gledaju is the 3rd person plural present tense form of gledati = to watch / to look at.

Because the subject is djeca = children, you need the they form:

• ja gledam = I watch
• ti gledaš = you watch
• on/ona gleda = he/she watches
• mi gledamo = we watch
• vi gledate = you watch
• oni/one/ona gledaju = they watch

Croatian does not need a separate word for are in a sentence like are watching. The present-tense verb form already carries that meaning.

So:

• Djeca gledaju can mean The children watch
• and also The children are watching

depending on context.

Yes. Very often, the Croatian present tense covers both meanings.

So:

• Djeca gledaju veliki mjehurić can mean
  The children watch a big bubble
  or
  The children are watching a big bubble

Usually the situation or context makes it clear which one is meant.

If you are translating into natural English, are watching is often the best choice for this sentence.

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

So djeca can mean:

• children
• the children

and veliki mjehurić can mean:

• a big bubble
• the big bubble

Context tells you which meaning is intended.

That is very normal in Croatian, so you should not look for a separate word matching English the or a.

Because mjehurić is a masculine singular inanimate noun, and here it is the direct object of the verb gledaju.

In Croatian, masculine singular inanimate nouns usually have the same form in:

• nominative
• accusative

So:

• veliki mjehurić = nominative
• veliki mjehurić = accusative

That is why nothing changes here.

Compare that with a masculine animate noun, where the accusative does change:

• veliki pas = a big dog, nominative
• vidim velikog psa = I see a big dog, accusative

So in your sentence, mjehurić is inanimate, which is why the form stays veliki mjehurić.

Because it is the direct object of gledaju.

The children are watching what?
→ veliki mjehurić

That makes mjehurić the direct object, so it should be in the accusative.

But for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular. So even though the form does not visibly change, the grammatical role still does.

You can think of it like this:

• function: accusative
• shape: looks the same as nominative

Because u can take different cases depending on meaning.

Here it means location:
in the park

When u means in / inside / at a place, it normally takes the locative case.

So:

• park = nominative
• u parku = in the park (locative)

But if you are talking about movement into a place, Croatian usually uses u + accusative:

• Idem u park = I am going to the park

So the contrast is:

• u parku = in the park, location
• u park = into the park, movement

Yes. Croatian word order is more flexible than English word order because case endings help show what each word is doing.

The neutral order here is:

• Djeca gledaju veliki mjehurić u parku.

But you could also say:

• U parku djeca gledaju veliki mjehurić.
• Veliki mjehurić djeca gledaju u parku.

These versions are possible, but they change the emphasis or sound more marked.

For a learner, the safest choice is to keep the neutral order:

• subject + verb + object + place

A rough English-friendly guide:

• Djeca ≈ dye-tsa
• gledaju ≈ GLEH-da-yoo
• veliki ≈ VEH-lee-kee
• mjehurić ≈ mye-HOO-rich
• u parku ≈ oo PAR-koo

A few useful notes:

• dj in djeca is a soft sound, roughly like dy said quickly
• j is pronounced like English y
• ć is a soft ch/t-type sound; English does not have an exact match
• Croatian stress can vary, but the above guide is good enough for a beginner

If you want to sound natural, try to pronounce each vowel clearly:

• e as in bet
• a as in father
• u as oo
• i as ee