U kutiji smo pronašli mali dar.

Because kutiji is the locative singular form of kutija (box).

After the preposition u when it means in, Croatian uses the locative case for location:

• kutija = box
• u kutiji = in the box

So U kutiji means in the box.

Croatian makes a difference between location and movement:

• u kutiji = in the box (location, so locative)
• u kutiju = into the box (movement toward/into, so accusative)

In your sentence, the gift was found inside the box, not moved into it, so u kutiji is correct.

Croatian past tense is often made with:

• a form of biti (to be)
• plus the l-participle

Here:

• smo = we are / we have as the auxiliary
• pronašli = past participle-like form of find

Together, smo pronašli = we found

The reason they are separated is that smo is a clitic, and clitics usually go in the second position of the sentence or clause. Since U kutiji comes first, smo comes right after it:

• U kutiji smo pronašli mali dar.

Yes. Croatian word order is fairly flexible.

These are all possible, with slightly different emphasis:

• U kutiji smo pronašli mali dar.
• Pronašli smo mali dar u kutiji.
• Mali dar smo pronašli u kutiji.

The version with U kutiji first highlights the location first: In the box, we found a small gift.

So the meaning stays basically the same, but the focus changes.

Because Croatian usually drops subject pronouns when they are already clear from the verb.

Here, smo already tells you the subject is we, so mi is unnecessary.

• smo pronašli = we found
• mi smo pronašli = we found too, but with extra emphasis on we

So the sentence without mi is the normal, natural version.

Pronašli agrees with the subject in number and sometimes gender.

In this sentence:

• smo tells us the subject is we
• pronašli is the masculine plural/default form

That means this form is used when:

• the group is all male, or
• the group is mixed, or
• gender is not being specified in a general/default way

If the speakers were all female, you would say:

• U kutiji smo pronašle mali dar.

So pronašli helps show who is doing the action.

It actually is in the object case, the accusative. It just happens to look the same.

Dar is a masculine inanimate noun. In Croatian, for masculine inanimate nouns:

• nominative singular = accusative singular

So:

• dar = gift
• mali dar = small gift

The adjective mali also matches the noun, and for masculine inanimate singular accusative it also looks the same as nominative.

That is why the object form does not visibly change here.

Yes. That is an important Croatian pattern.

For masculine animate nouns, the accusative singular usually changes and looks like the genitive.

Compare:

• Vidim mali dar. = I see a small gift.
  (dar is inanimate, so no visible change)

But:

• Vidim malog psa. = I see a small dog.
  (pas is animate, so accusative changes to psa, and mali changes to malog)

So mali dar stays the same because dar is inanimate.

In Croatian, adjectives usually come before the noun they describe.

So:

• mali dar = small gift

The adjective must agree with the noun in:

• gender
• number
• case

Here both are:

• masculine
• singular
• accusative (same visible form as nominative because the noun is inanimate)

So mali dar is a normal adjective + noun combination.

No. Croatian does not use articles like English a/an/the.

So mali dar can mean:

• a small gift
• the small gift

Which one is meant depends on context.

That is why one Croatian sentence can correspond to more than one natural English translation.

Both dar and poklon can mean gift/present.

Very roughly:

• poklon is often the more everyday word for a present
• dar can sound a bit more formal, literary, or elevated, though it is still a normal word

So mali dar is perfectly correct, but in casual speech you may also often hear:

• mali poklon

Both are good; the nuance depends on context and style.

The basic verb is pronaći, which means to find.

In the sentence, pronašli is the past form used with smo:

• pronaći = to find
• smo pronašli = we found

You may also encounter naći, which is a closely related and very common verb also meaning to find. In many contexts, naći and pronaći are quite similar, though pronaći can sometimes sound a bit more like discover/find successfully.

So in this sentence:

• U kutiji smo pronašli mali dar. = We found a small gift in the box.