A meno che il gallo non si spaventi, i pulcini restano vicino alla gallina.

A meno che means unless or except if. It introduces an exception to what is stated in the main clause.

So the structure is:

• A meno che + clause
• main clause

In this sentence:

• A meno che il gallo non si spaventi = Unless the rooster gets frightened
• i pulcini restano vicino alla gallina = the chicks stay near the hen

A very important grammar point: after a meno che, Italian normally uses the subjunctive.

This non is a very common feature after expressions like a meno che. It is called pleonastic non or expletive non.

That means:

• it looks like a negative
• but it does not actually make the clause negative

So here, non si spaventi does not mean does not get frightened. It still means gets frightened.

This is normal in standard Italian after a meno che:

• A meno che tu non venga... = Unless you come...
• A meno che lui non sappia... = Unless he knows...

A learner should usually treat a meno che ... non + subjunctive as a fixed pattern.

Because a meno che requires the subjunctive, not the indicative.

Here the verb is spaventarsi = to get frightened / to become scared.

Its present subjunctive, third person singular, is:

• che io mi spaventi
• che tu ti spaventi
• che lui/lei si spaventi

So:

• il gallo si spaventa = indicative
• che il gallo si spaventi = subjunctive

After a meno che, Italian uses the second pattern.

Si is the reflexive pronoun from the verb spaventarsi.

Compare:

• spaventare qualcuno = to frighten someone
• spaventarsi = to get frightened / to become scared

So:

• Il rumore spaventa il gallo = The noise frightens the rooster
• Il gallo si spaventa = The rooster gets frightened

In your sentence, the rooster is the one experiencing the fear, so Italian uses the reflexive form spaventarsi.

The main clause states a general fact or usual result, so the present indicative is natural:

• i pulcini restano vicino alla gallina

This is like saying what normally happens.

Italian often uses the present tense this way for general truths, habits, or repeated situations.

If you were talking about one specific future situation, you might also find a future tense in some contexts, but here the present sounds like a general rule.

Italian uses definite articles much more often than English.

With animals, people, and nouns in general, Italian often includes the article where English might not focus on it as much.

So:

• il gallo = the rooster
• i pulcini = the chicks
• la gallina = the hen

In a sentence like this, the articles sound completely normal and expected.

Because vicino normally takes the preposition a before a noun or pronoun when it means near.

So the pattern is:

• vicino a + noun

Examples:

• vicino alla casa = near the house
• vicino al fiume = near the river
• vicino a me = near me

In your sentence:

• vicino a la gallina becomes vicino alla gallina

because a + la = alla.

Alla is a contraction of:

• a + la = alla

Italian often combines prepositions with definite articles:

• a + il = al
• a + lo = allo
• a + la = alla
• a + i = ai
• a + gli = agli
• a + le = alle

So vicino alla gallina literally contains near to the hen.

Good question. Here vicino is being used in an adverbial way, so it stays invariable.

That is very common after verbs like:

• stare
• restare
• rimanere

So:

• i pulcini restano vicino alla gallina = perfectly natural

You may also hear vicini in other contexts when vicino is treated more clearly as an adjective:

• I pulcini sono vicini alla gallina

So in short:

• vicino can be invariable when used adverbially
• vicini appears when it behaves as a normal adjective agreeing with a plural noun

In your sentence, vicino is fine and natural.

Yes. Italian can reverse the order:

• I pulcini restano vicino alla gallina, a meno che il gallo non si spaventi.

This means the same thing.

The version with A meno che... first simply puts the exception first. The comma helps separate the subordinate clause from the main clause.

Yes, often it could.

• restano vicino alla gallina
• rimangono vicino alla gallina

Both can mean stay/remain near the hen.

In many contexts, restare and rimanere are very close in meaning.
The choice is often stylistic or based on preference, though some speakers may feel small differences depending on context.

In this sentence, restano sounds perfectly normal and natural.