Se ektondros dum la nokto, la infanoj venos al nia ĉambro.

It is made of three parts:

• tondr- = thunder
• ek- = begin suddenly, start to
• -os = future tense

So ektondros means something like will start thundering or there will suddenly be thunder.

The prefix ek- adds the idea of the beginning of an action. Without it, tondros would simply mean will thunder, with less emphasis on the sudden start.

Esperanto does not use a dummy subject the way English does in weather expressions.

English says:

• It is raining
• It is thundering

But in Esperanto, you can simply say:

• Pluvas
• Tondras

So ektondros is complete by itself. There is no need for a separate word meaning English it.

This is a very common question for English speakers.

Esperanto does not follow the English rule that after if you normally avoid the future tense. In Esperanto, the tense usually matches the time you really mean.

Here both actions are in the future:

• the thunder may happen in the future
• the children’s coming will happen in the future

So Se ektondros ..., la infanoj venos ... is perfectly natural.

English would usually say If it thunders during the night, the children will come..., but Esperanto is free to use the future in both parts.

Dum means during.

So dum la nokto means during the night.

It focuses on the event happening at some time within that period. In this sentence, it means that if the thunder starts at some point during the night, then the children will come.

A learner might compare it with en la nokto. That can also refer to in the night / at night, but dum clearly highlights the time span during the night.

Because la makes it a specific night-period: the night.

In context, this usually means the coming night or that night under discussion, not just night in a general sense.

Without la, dum nokto would sound more like during a night or would feel less natural here.

Because the sentence begins with a subordinate clause introduced by se.

• Se ektondros dum la nokto = conditional clause
• la infanoj venos al nia ĉambro = main clause

In Esperanto, commas are commonly used to separate clauses, especially when the subordinate clause comes first. So the comma here is normal and expected.

Because veni means come, while iri means go.

The difference depends on viewpoint.

• veni = movement toward the speaker or the reference point
• iri = movement away from that point

Since the destination is nia ĉambro — our room — the movement is toward the speaker’s location or shared reference point, so venos is the natural choice.

Both can work, but they focus slightly differently.

• al nia ĉambro = to our room
• en nian ĉambron = into our room

So:

• veni al nia ĉambro emphasizes the destination
• veni en nian ĉambron emphasizes entering into the room

In this sentence, al nia ĉambro is a simple and natural way to express where they will come.

Because the phrase uses the preposition al.

After a preposition like al, the noun normally stays in the basic form, not the accusative:

• al nia ĉambro

If you used en to show movement into a place, then you would often use the accusative:

• en nian ĉambron

So the lack of -n here is completely correct.

La means the, so la infanoj means the children.

This suggests specific children already known from the situation or context — for example, the family’s children.

If you said just infanoj, it would sound more general, like children as a category, not a particular group.

Yes. Esperanto word order is fairly flexible.

For example, you could also say:

La infanoj venos al nia ĉambro, se ektondros dum la nokto.

That has the same basic meaning. The original version puts the condition first, which is very natural because it sets up the situation before giving the result.

Often, but not always in a rigid word-for-word way.

The prefix ek- usually adds one of these ideas:

• the beginning of an action
• suddenness
• a brief onset

So with ektondros, will start thundering is a good explanation. But depending on context, English might express it differently, such as if thunder suddenly begins or if it starts to thunder.

The important thing is the nuance: something begins suddenly.