Nas dvoje večeras čuvamo nećaka i nećakinju.

Nas dvoje means the two of us and is more specific than mi (we).

• mi čuvamo = we are looking after / babysitting
• nas dvoje čuvamo = the two of us are looking after / babysitting

So the speaker is emphasizing that exactly two people are involved.

This is a very common Croatian pattern:

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

It is especially used when talking about a mixed pair or when gender is not the main point.

Croatian usually uses the oblique form of the pronoun in this construction:

• nas dvoje
• vas dvoje
• njih dvoje

Even though nas is also the form you may know as us, here it is simply the standard form used with dvoje.

So nas dvoje is the normal idiomatic way to say the two of us.
You may occasionally hear mi dvoje, but nas dvoje is the more standard and common form in this kind of sentence.

Dvoje is a collective numeral meaning two as a pair/group.

It is often used:

• for mixed-gender groups
• for children
• for some nouns that naturally come in grouped counting patterns
• when talking about people as a pair rather than simply counting individuals

Here, nas dvoje refers to two people together.

Compare:

• dva muškarca = two men
• dvije žene = two women
• nas dvoje = the two of us

So dvoje is not just a simple replacement for dva/dvije; it has its own special uses.

Because the subject is nas dvoje = the two of us, the verb agrees with we.

So:

• čuvam = I look after
• čuvaš = you look after
• čuvamo = we look after

Even though nas dvoje contains the word nas, the meaning is still we two, so the verb must be plural:

• Nas dvoje čuvamo...

The verb čuvati can mean several related things, depending on context:

• to guard
• to keep safe
• to look after
• to take care of
• to babysit

In this sentence, because the objects are nećaka i nećakinju (nephew and niece), the natural meaning is:

• we’re looking after
• we’re babysitting

So this is not about guarding them like security guards; it is ordinary childcare / supervision.

They are in the accusative case because they are the direct objects of čuvamo.

The verb answers whom are we looking after?

• nećaka = nephew
• nećakinju = niece

Dictionary forms:

• nećak = nephew
• nećakinja = niece

Accusative forms here:

• nećak → nećaka
• nećakinja → nećakinju

So:

• čuvamo nećaka i nećakinju = we are looking after a/the nephew and niece

Because nećak is a masculine animate noun, and masculine animate nouns usually change in the accusative singular.

So:

• nominative: nećak
• accusative: nećaka

This is a very important Croatian pattern:

• vidim brata = I see my brother
• imam brata = I have a brother
• čuvamo nećaka = we’re looking after our nephew

If it were an inanimate masculine noun, the accusative would usually look like the nominative instead.

Because nećakinja is a feminine noun, and feminine nouns ending in -a usually change to -u in the accusative singular.

So:

• nominative: nećakinja
• accusative: nećakinju

The same pattern appears in many feminine nouns:

• sestra → sestru
• prijateljica → prijateljicu
• nećakinja → nećakinju

Yes, very often Croatian leaves possession unstated when it is obvious from context.

So nećaka i nećakinju can naturally be understood as:

• our nephew and niece
• or simply the nephew and niece, depending on context

In family contexts, English often requires our, but Croatian can omit it if the relationship is clear.

If you wanted to state it explicitly, you could say:

• Nas dvoje večeras čuvamo svog nećaka i svoju nećakinju.

But that is not necessary in normal conversation.

Večeras means this evening / tonight.

It refers specifically to the evening of the current day or the coming evening, depending on context.

Examples:

• Dolazim večeras. = I’m coming tonight.
• Što radiš večeras? = What are you doing tonight?

In this sentence, it tells you when the action is happening:

• Nas dvoje večeras čuvamo nećaka i nećakinju.

Croatian word order is fairly flexible. The sentence given is natural, but other orders are also possible depending on emphasis.

For example:

• Nas dvoje večeras čuvamo nećaka i nećakinju.
• Večeras nas dvoje čuvamo nećaka i nećakinju.
• Nećaka i nećakinju večeras čuvamo nas dvoje.

The original version sounds neutral and natural.
Putting večeras first can emphasize tonight.
Putting nas dvoje later can emphasize we two, as opposed to someone else.

So the word order is not random, but it is more flexible than in English.

Not in this exact expression.

You would not normally say nas dva in standard Croatian to mean the two of us in this general sense. The idiomatic phrase is nas dvoje.

Dva/dvije are the ordinary numerals for counting nouns:

• dva muškarca = two men
• dvije žene = two women

But with personal pronouns in this kind of phrase, Croatian normally uses dvoje:

• nas dvoje
• vas dvoje
• njih dvoje

This sentence has both sounds, and learners often ask about them.

• č is a harder sound, roughly like ch in church
• ć is softer, a palatal sound that English does not have exactly

In this sentence:

• č appears in čuvamo
• ć appears in nećaka and nećakinju

For many learners, the key point is simply that Croatian treats them as different sounds and different letters, so spelling matters.

Yes, there can be a slight difference in nuance.

• čuvati often means look after / keep safe / babysit
• paziti often means watch out for / pay attention to / take care of

In many everyday situations, both can work when talking about children:

• Čuvamo djecu.
• Pazimo na djecu.

But čuvati nekoga is very natural for babysitting / taking care of someone, which is why it fits this sentence well.

Each noun is singular in form, but together they refer to two people.

So literally it is:

• a nephew and a niece or, in context,
• our nephew and niece

Croatian often lists family members this way rather than using a combined plural noun. It is completely normal.

You can still use nas dvoje in many contexts for the two of us, but Croatian also has gender-sensitive forms when you want to be specific:

• nas dvije = the two of us, if both are female
• nas dvojica = the two of us, if both are male

So possible versions are:

• Nas dvije večeras čuvamo nećaka i nećakinju. = The two of us women are babysitting our nephew and niece tonight.
• Nas dvojica večeras čuvamo nećaka i nećakinju. = The two of us men are babysitting our nephew and niece tonight.

The original nas dvoje is especially natural for a mixed pair or when the focus is simply on two of us.