Как только зазвучала музыка, дети начали танцевать.

It is a fixed expression: как только = as soon as.

Even though it is made of two words, learners should usually treat it as one conjunction introducing a subordinate clause:

• Как только зазвучала музыка... = As soon as the music started playing...

You can think of it as a time-linking expression, similar to when but more immediate. It emphasizes that the second action happened right after the first one.

Because Как только зазвучала музыка is a subordinate clause, and Russian separates subordinate clauses from the main clause with a comma.

So the structure is:

• Как только зазвучала музыка, = subordinate clause
• дети начали танцевать. = main clause

This is very similar to English punctuation in a sentence like:

• As soon as the music started, the children began to dance.

If the subordinate clause comes first, the comma is required.

Зазвучала is the past tense of зазвучать, which is a perfective verb.

The prefix за- often adds the idea of beginning. So:

• звучать = to sound, to be playing/sounding
• зазвучать = to begin to sound, to start playing

That is why зазвучала музыка means something like:

• the music started playing
• the music began to sound

If you used звучала, that would describe the music as already sounding/playing, not the moment it started.

Because the subject is музыка, and музыка is a feminine singular noun.

In the past tense, Russian verbs agree with the subject in gender and number:

• masculine: зазвучал
• feminine: зазвучала
• neuter: зазвучало
• plural: зазвучали

Since музыка is feminine singular, the correct form is зазвучала.

Дети is the nominative plural form, because it is the subject of начали.

Here:

• дети = the children
• начали = began

So дети is doing the action.

A helpful thing to remember is that дети is an irregular plural form of ребёнок. It does not look like a regular plural, so learners often pause at it.

Because Russian often uses начать + infinitive to mean to begin doing something.

So:

• начали танцевать = began to dance

This is very natural Russian.

Compare:

• дети танцевали = the children were dancing / danced
• дети начали танцевать = the children started dancing

The sentence is focusing on the start of the dancing, not just the fact that dancing happened.

After начать, Russian usually uses the infinitive of the action, and very often that infinitive is imperfective when the focus is simply on starting the activity.

So:

• начали танцевать = began dancing

The idea is not that they completed a single dance; it is that they entered into the activity of dancing.

This is why танцевать is more natural here than a perfective verb.

Because the whole sentence describes two events that happened in the past:

1. the music started
2. the children began to dance

Russian past tense works a little differently from English, because aspect does a lot of the work that English sometimes expresses with different tenses.

Here both verbs are past, but each also gives a specific event:

• зазвучала = the music started playing
• начали = the children started dancing

So the sentence tells a sequence of completed past events.

Both can introduce a time clause, but как только is more specific and immediate.

• Когда зазвучала музыка, дети начали танцевать. = When the music started, the children began to dance.
• Как только зазвучала музыка, дети начали танцевать. = As soon as the music started, the children began to dance.

So как только emphasizes that the second action followed the first one right away.

Yes. Russian word order is flexible, though the neutral order here is very natural.

You could also say:

• Дети начали танцевать, как только зазвучала музыка.

This means the same thing: The children began to dance as soon as the music started playing.

The difference is mainly in emphasis:

• clause first: emphasizes the trigger/event first
• main clause first: emphasizes the children’s action first

Both are correct.

It is literally music, but in Russian this is a very normal way to say the music started playing.

So зазвучала музыка sounds natural and idiomatic. Russian often uses the noun directly as the subject of the verb:

• зазвучала музыка = the music started playing
• literally: the music began to sound

English usually prefers the music started or the music began to play, while Russian naturally says it this way.

Yes, you can.

Both are grammatical:

• Как только зазвучала музыка, дети начали танцевать.
• Как только музыка зазвучала, дети начали танцевать.

The version with the verb first, зазвучала музыка, is very natural in narrative style and often sounds a bit more dynamic, especially when introducing an event.

So this is more about style and information flow than basic grammar.

A natural stress pattern would often highlight the important events:

• Как только зазвуча́ла музыка, де́ти нача́ли танцева́ть.

Useful stress points:

• как только
• зазвуча́ла
• музыка
• де́ти
• нача́ли
• танцева́ть

If spoken naturally, the strongest stress often falls on the verbs or the key new information. In this sentence, the important sequence is:

1. the music started
2. the children started dancing

So those actions often receive clear emphasis.