Copiii sunt înăuntru.

Because Romanian is combining:

• copil = child
• copii = children
• copiii = the children

Romanian often puts the definite article at the end of the noun instead of using a separate word like English the.

So here the form works like this:

• copil → child
• copii → children
• copiii → the children

That is why you see three i's:

• one belongs to the stem/plural formation,
• one is part of the plural ending,
• and one comes from the definite article.

It is pronounced roughly like ko-PI-ee-ee, but in normal speech the vowels flow together smoothly.

A useful way to think of it is:

• copii = ko-PII
• copiii = ko-PII-ee

The stress falls on pi: co-PI-ii.

For many English speakers, the hard part is not skipping one of the i sounds. Even if they are not all pronounced as completely separate syllables in fast speech, the definite form is still audibly longer than copii.

Because Romanian usually attaches the definite article directly to the noun.

Compare:

• copii = children
• copiii = the children

This is a very important feature of Romanian grammar. English says the children, but Romanian usually says one word: copiii.

Sunt is the present tense form of a fi = to be.

In this sentence, sunt means are.

So:

• eu sunt = I am
• tu ești = you are
• el/ea este / e = he/she is
• noi suntem = we are
• voi sunteți = you are
• ei/ele sunt = they are

Since copiii is plural, Romanian uses sunt.

Because copiii is a third-person plural subject: the children = they.

So Romanian uses the plural form:

• Copilul este... = The child is...
• Copiii sunt... = The children are...

The verb has to agree with the subject in number.

Înăuntru is usually an adverb, meaning inside / indoors / in depending on context.

In Copiii sunt înăuntru, it tells you where the children are.

So the structure is:

• Copiii = subject
• sunt = verb
• înăuntru = adverb of place

Romanian can also use other words for location, but înăuntru is a very common everyday way to say inside.

They are similar, but not always identical in tone.

• înăuntru is very common, everyday, and natural in speech.
• în interior also means inside / in the interior, but it can sound a bit more formal or more literal depending on context.

For a basic sentence like this, Copiii sunt înăuntru is the most natural everyday phrasing.

Yes, often it can.

Romanian frequently drops subject pronouns and sometimes relies on context. So if it is already clear who is being talked about, Sunt înăuntru can mean They are inside.

However, Copiii sunt înăuntru is clearer and more explicit because it names the subject directly: the children.

The normal word order here is:

• Copiii sunt înăuntru.

This is the most neutral way to say it.

Romanian does allow some flexibility in word order, but changing the order can change emphasis or make the sentence sound less neutral.

For example:

• Copiii sunt înăuntru. = neutral statement
• Înăuntru sunt copiii. = more emphasis on inside or on contrast
• Sunt copiii înăuntru? = Are the children inside? (question intonation / question structure)

So the given order is the standard one for a simple statement.

The diacritics show important Romanian vowel sounds.

In înăuntru:

• î represents a central vowel sound that English does not really have
• ă represents the schwa sound, like the a in English sofa

These marks are not decorative—they are part of the correct spelling and pronunciation.

So it is important to write:

• înăuntru ✅

and not a version without diacritics, unless you absolutely cannot type them.

In this sentence, copiii specifically means the children, not just children in a general sense.

If you wanted the indefinite plural children, Romanian would normally use:

• copii

So the contrast is:

• Copii sunt înăuntru = Children are inside / some children are inside (less definite, and often less natural without context)
• Copiii sunt înăuntru = The children are inside

In the given sentence, the speaker is talking about a specific group of children.