Kad djeca napokon zaspu, nas dvoje sjednemo na terasu i kažemo da je dan prošao bolje nego što smo očekivali.

Both kad and kada mean when.

• kad is the shorter, very common everyday form
• kada is a bit fuller and can sound slightly more formal or emphatic

In this sentence, Kad djeca napokon zaspu... is completely natural and idiomatic.

Because Kad djeca napokon zaspu is a subordinate time clause: When the children finally fall asleep.

In Croatian, if this kind of subordinate clause comes before the main clause, it is normally separated by a comma:

• Kad djeca napokon zaspu, nas dvoje sjednemo...

That is very similar to English:

• When the children finally fall asleep, the two of us sit down...

This is a very important Croatian pattern.

zaspati is a perfective verb, and zaspu is its present-tense form. But with perfective verbs, the present tense often refers to a completed future event or a repeated sequence.

So:

• Kad djeca napokon zaspu = When the children finally fall asleep
• not when they are falling asleep

Here it describes the point at which the action is completed.

Compare:

• spavaju = they are sleeping / they sleep
• zaspu = they fall asleep

napokon means finally / at last.

Here it modifies zaspu:

• Kad djeca napokon zaspu = When the children finally fall asleep

Its position is flexible, but this placement is very natural. It usually goes near the verb or the part of the clause it emphasizes.

For example:

• Djeca napokon zaspu
• Napokon djeca zaspu

But the version in your sentence sounds especially natural.

nas dvoje is a common Croatian way to say the two of us.

It is built from:

• nas = us
• dvoje = a collective numeral meaning two people

So literally it is something like us two.

This structure is very common with people:

• nas dvoje = the two of us
• vas dvoje = the two of you
• njih dvoje = the two of them

It often refers to a pair, especially a mixed-gender pair or simply two people viewed together as a unit.

Croatian often leaves the subject unstated, because the verb ending already shows the person and number:

• sjednemo = we sit down

So sjednemo alone would already be grammatical.

But nas dvoje is added for emphasis or clarity:

• it highlights that it is specifically the two of us
• it gives a more intimate, scene-setting feeling

So:

• sjednemo = we sit down
• nas dvoje sjednemo = the two of us sit down

Because sjednemo comes from a verb meaning sit down, not be sitting.

So the contrast is:

• sjesti / sjednuti → to sit down
• sjediti → to sit / be sitting

That affects the case after na:

• na terasu with accusative = movement toward a place
• na terasi with locative = being at/on the terrace

So:

• sjednemo na terasu = we go sit down on the terrace
• sjedimo na terasi = we are sitting on the terrace

Even though English says sit on the terrace, Croatian treats sit down as movement into that position.

Because na can take different cases depending on meaning:

• accusative for direction/movement toward a place
• locative for location in/at/on a place

Here, the idea is movement:

• sjednemo na terasu = we sit down onto/out to the terrace

So terasa becomes terasu.

Compare:

• Idemo na terasu. = We’re going out to the terrace.
• Sjedimo na terasi. = We’re sitting on the terrace.

kažemo da... means we say that...

In Croatian, after verbs like reći / kazati (to say), it is very common to introduce the content with da:

• kažemo da je... = we say that...

This is the normal way to report a statement.

Here it means that the two people say to each other, or remark, that the day turned out better than expected.

This is a da-clause with the perfect tense of proći.

Breakdown:

• da = that
• je = is / has, here the auxiliary for the perfect tense
• dan = day
• prošao = passed / gone by

So:

• da je dan prošao bolje... = that the day went better...

The subject is dan, so the participle is masculine singular:

• prošao agrees with dan

This is the normal Croatian perfect tense structure.

Croatian clitic auxiliaries such as je, sam, smo, su usually go in second position in their clause, not necessarily directly after the subject.

So:

• da je dan prošao...

is normal because je is placed early in the clause as a clitic.

Croatian word order is more flexible than English, but clitics have special placement rules. You will often see:

• On je došao.
• Mislim da je on došao.

not usually da on je došao.

This is the standard Croatian comparative pattern:

• bolje = better
• nego što = than
• smo očekivali = we expected

So the whole phrase means:

• better than we expected

The što is very common here and makes the comparison explicit and natural.

Compare:

• veće nego što sam mislio = bigger than I thought
• teže nego što izgleda = harder than it looks

Because the subject of smo očekivali is we:

• smo = we have
• očekivali = expected

In the Croatian perfect tense, the participle agrees with the subject in number and gender.

Here the subject is the implied we, referring back to nas dvoje. For a mixed pair, or when gender is not being specifically marked in another way, standard Croatian normally uses the masculine plural form:

• smo očekivali

If two women were speaking, you could hear:

• smo očekivale

But in a sentence like this, očekivali is the expected standard form.

Because Croatian has no articles like a/an/the.

So nouns appear without an article, and definiteness is understood from context:

• djeca = children / the children
• dan = day / the day
• terasu = a terrace / the terrace

In this sentence, context makes them definite:

• djeca = the children
• dan = the day
• terasu = the terrace

It can naturally suggest a habitual repeated situation.

The whole sentence feels like a regular scene in family life:

• When the children finally fall asleep, the two of us sit on the terrace and say...

Croatian often uses present forms like this for repeated events or typical sequences. Depending on context, it could also refer to one specific occasion, but without more context it strongly sounds like a recurring pattern.

Technically you may sometimes see a simpler translation like we sit, but we sit down is more accurate.

That is because sjednemo comes from a verb of entering the sitting position, not simply being seated.

So the best sense here is:

• the two of us sit down on the terrace

If you wanted we are sitting on the terrace, Croatian would more naturally use sjedimo na terasi.