U našoj školi redovito održavaju male radionice za roditelje i djecu.

Because after u when it means in/at a place, Croatian uses the locative case.

• nominative: naša škola = our school
• locative: u našoj školi = in/at our school

Both the adjective naša and the noun škola change form to match the locative.

Because škola is a feminine singular noun, and in the locative singular the adjective must agree with it.

So:

• naša škola = nominative
• u našoj školi = locative

This is adjective-noun agreement: gender, number, and case all have to match.

That is the locative singular ending of the noun škola.

• nominative: škola
• locative: u školi

Many feminine nouns ending in -a change to -i in the locative singular.

Redovito is an adverb meaning regularly.

It comes from the adjective redovit = regular.

Compare:

• redovit program = a regular program
• redovito održavaju = they hold regularly / they regularly hold

So it describes how often the workshops are held.

Croatian often leaves out the subject when it is understood from the verb form.

Održavaju is 3rd person plural, so literally it means they hold / they organize.

In sentences like this, Croatian often uses this form in a general, unspecified way:

• U našoj školi redovito održavaju... = At our school, they regularly hold...

It does not necessarily mean a specific they; it can mean something like people/the school/staff regularly organize.

Yes. That would be a very natural alternative.

• Redovito održavaju male radionice... = They regularly hold small workshops...
• Male radionice se redovito održavaju... = Small workshops are regularly held...

The version with se sounds more impersonal or passive-like. The original sentence uses an active verb with an unspecified they.

Because male radionice is the direct object of održavaju, so it is in the accusative plural.

• singular nominative: mala radionica
• plural nominative: male radionice
• plural accusative: male radionice

For feminine plural inanimate nouns, nominative and accusative often look the same, which is why the form does not change here.

Because the sentence is talking about workshops in general, not just one workshop.

• radionica = workshop
• radionice = workshops

So male radionice means small workshops.

Here za means for in the sense of intended for.

After za, Croatian uses the accusative case:

• za roditelje
• za djecu

So the phrase means for parents and children.

Because roditelji is a masculine animate plural noun, and after za it must go into the accusative plural.

• nominative plural: roditelji = parents
• accusative plural: roditelje

Masculine animate nouns usually have a special accusative form like this.

Because after za, the noun must be in the accusative.

• nominative: djeca = children
• accusative: djecu

This is an important word to memorize because djeca is somewhat irregular. It behaves as a plural word meaning children, but its case forms are not as simple as many regular nouns.

Croatian word order is fairly flexible.

This sentence puts redovito before the verb, which is very natural:

• U našoj školi redovito održavaju male radionice...

But other orders are also possible, depending on emphasis, for example:

• U našoj školi održavaju redovito male radionice...
• Male radionice za roditelje i djecu u našoj školi redovito održavaju.

The original order sounds neutral and natural.

Because Croatian has no articles.

So:

• škola can mean school, a school, or the school
• radionice can mean workshops, some workshops, or the workshops

You understand the exact meaning from context rather than from articles.

Usually at our school sounds more natural in English for this kind of sentence.

Croatian u literally means in, but English often uses at with institutions and events:

• U našoj školi... → At our school...

So both can make sense, but at our school is often the best natural translation.