Kad prelazi cestu, djevojčica čvrsto stisne maminu ruku.

Yes. Kad means when.

In this sentence, Kad prelazi cestu means When she crosses the road or When crossing the road.

Croatian also has kada, which means the same thing. Kad is simply the shorter and very common form.

The subject is understood from the rest of the sentence: it is djevojčica.

Croatian often leaves out pronouns and other repeated subjects when they are clear from context. So:

• Kad prelazi cestu = When she crosses the road
• the she is not stated, but it is understood to be the little girl

This is very normal in Croatian.

Croatian often uses the present tense for repeated, habitual, or general actions, just like English can:

• When she crosses the road, she holds her mother’s hand.

So prelazi is present tense, but it does not have to mean right now at this moment. It can describe something that regularly happens.

Because cestu is in the accusative case.

The verb prelaziti / prijeći (to cross) takes a direct object, and that object goes into the accusative:

• cesta = road (nominative, dictionary form)
• cestu = road (accusative)

So:

• prelazi cestu = crosses the road

This is similar to English using a direct object after cross.

In Croatian, prelaziti directly takes the thing being crossed as its object, with no preposition.

So you say:

• prelaziti cestu = to cross the road
• not something like prelaziti preko cestu

You can use preko in other structures, but with prelaziti cestu, the normal pattern is just verb + accusative object.

Djevojčica means little girl or young girl.

It is more specific than a general English girl. It refers to a child, not a teenage girl or young woman.

So the sentence is clearly about a child.

Čvrsto means firmly or tightly.

It is an adverb, and it modifies the verb stisne:

• čvrsto stisne = squeezes/grips tightly

So it tells you how she squeezes the hand.

This is a very useful question, because it involves aspect.

• stisnuti = perfective, to squeeze/grip once, as a complete act
• stiskati / stis(k)ati or stiskati / stišće-type imperfective forms = to be squeezing, to squeeze repeatedly/continuously

Here stisne presents the action as a single complete act: each time she crosses the road, she gives her mother’s hand a firm squeeze.

So the sentence has a sense like:

• When she crosses the road, the little girl gives her mother’s hand a tight squeeze.

If you used stišće, it would sound more like an ongoing action:

• she is holding/squeezing it continuously

Both kinds of wording can be possible in Croatian, but stisne focuses more on the completed act.

Maminu is a possessive adjective made from mama (mum/mom).

So:

• mamina ruka = mum’s hand
• maminu ruku = accusative form, because it is the object of stisne

Croatian often uses possessive adjectives like this with family members:

• mamin = mum’s
• tatin = dad’s
• bakin = grandma’s

You could also say ruku svoje mame or sometimes ruku majke, depending on style and meaning, but maminu ruku is very natural and warm in tone.

Because they must agree in case, gender, and number.

Here:

• ruka is feminine singular
• as the direct object, it becomes accusative singular: ruku
• the possessive adjective must match it: mamina → maminu

So:

• maminu ruku = both words are feminine singular accusative

This kind of agreement is a basic and very important feature of Croatian grammar.

Because Kad prelazi cestu is a subordinate clause placed before the main clause.

Croatian normally separates that kind of introductory clause with a comma:

• Kad prelazi cestu, djevojčica čvrsto stisne maminu ruku.

This is very similar to English punctuation in sentences like:

• When she crosses the road, the little girl tightly squeezes her mother’s hand.

Croatian word order is fairly flexible.

This sentence is natural because it first sets the time situation, then gives the main action:

• Kad prelazi cestu, djevojčica čvrsto stisne maminu ruku.

But other word orders are possible, depending on emphasis. For example, you might also hear variants that emphasize the subject or object differently.

Still, the given order is very normal and easy to understand:

1. when the action happens
2. who does it
3. how
4. what she squeezes

More naturally, mama corresponds to mum/mom, not the more formal mother.

So maminu ruku is best understood as:

• her mom’s hand
• her mum’s hand

If the sentence used majka instead, it would sound more formal or neutral.