Na farmi smo svi dobili po jednu čašu soka i po jedan komad kolača.

Here po means each or apiece.

So:

• po jednu čašu soka = one glass of juice each
• po jedan komad kolača = one piece of cake each

It shows distribution: every person got the same amount.

It is repeated because there are two separate things being distributed:

• po jednu čašu soka
• po jedan komad kolača

Repeating po makes it very clear that each person got one of each item. It is natural and clear Croatian style here.

Croatian often uses na with certain places where English might say at or on, and farm is one of those places.

So:

• na farmi = at/on the farm

This is just the normal idiomatic choice in Croatian.

Also, because this means location and not movement, na is followed here by the locative case.

Farmi is locative singular of farma.

• base form: farma
• locative singular: farmi

After na meaning location, Croatian uses the locative:

• na farmi = at the farm

If you were talking about movement to the farm, you would use accusative instead:

• na farmu = to the farm

This is the normal Croatian past tense.

It is built with:

• the auxiliary biti in the present tense: smo = we are / we have as an auxiliary
• the past participle: dobili = got / received

Together:

• smo dobili = we got

So Croatian past tense often works like this:

• sam dobio/dobila
• si dobio/dobila
• je dobio/dobila
• smo dobili
• ste dobili
• su dobili

Because Croatian often leaves out subject pronouns when they are already clear from the verb.

Here smo already tells you the subject is we.

So:

• smo dobili already means we got

The word svi does not mean we. It means all. It adds the idea that all of us got something.

Svi means all.

So the sentence is not just we got..., but we all got...

Compare:

• Na farmi smo dobili... = At the farm, we got...
• Na farmi smo svi dobili... = At the farm, we all got...

It adds emphasis that nobody was left out.

Dobili agrees with the subject in number and gender.

Here it is plural masculine, which in Croatian is also the normal form for a mixed group or an unspecified group.

So:

• dobili = used for a group of men, or a mixed group
• dobile = used for a group of women only

If the speakers were all female, you would normally expect:

• Na farmi smo sve dobile...

Literally, they mean one.

Croatian does not have articles like English a or the.

So in English, you may translate:

• jednu čašu as a glass or one glass
• jedan komad as a piece or one piece

In this sentence, because of po, the meaning is specifically one each, so jednu/jedan really do carry the sense of one.

Because the nouns have different genders, and the number word jedan has to agree with them.

• čaša is feminine
• komad is masculine

Also, these phrases are in the accusative singular because they are direct objects of dobili.

So:

• jedna čaša → jednu čašu in accusative
• jedan komad → jedan komad in accusative

For masculine inanimate nouns like komad, the accusative is the same as the nominative. For feminine nouns like čaša, the accusative changes.

Because after words like čaša and komad, Croatian usually uses the genitive to mean of.

So:

• čaša soka = a glass of juice
• komad kolača = a piece of cake

This is very common with containers, quantities, and parts:

• šalica čaja = a cup of tea
• boca vode = a bottle of water
• komad kruha = a piece of bread

So soka and kolača are genitive forms.

Croatian word order is more flexible than English word order.

In this sentence:

• Na farmi is placed first to set the scene: At the farm
• smo is a clitic, and clitics normally come near the beginning of the clause, often in the second position
• svi comes after that and adds all

So Na farmi smo svi dobili... is a very natural order.

You could also hear:

• Svi smo na farmi dobili...
• Svi smo dobili...

But the given sentence emphasizes the location first.