La infanoj ludas en la salono dum la patrino preparas supon.

In Esperanto, -j marks the plural.

• infano = child
• infanoj = children

So la infanoj means the children.

The ending -as is the present-tense verb ending in Esperanto.

• ludas = play / are playing
• preparas = prepare / is preparing

A very useful point for English speakers: Esperanto verbs do not change for person.

• mi ludas = I play
• vi ludas = you play
• li ludas = he plays
• ili ludas = they play

So -as always means present tense, no matter who is doing the action.

Esperanto usually uses the simple present tense where English might use either play or are playing.

So:

• la infanoj ludas can mean the children play or the children are playing
• la patrino preparas can mean the mother prepares or the mother is preparing

Context tells you which English version sounds most natural.

The -n ending usually marks the direct object.

In this sentence:

• la patrino preparas supon = the mother is preparing soup

Here supon is the thing being prepared, so it gets -n.

But in:

• en la salono = in the living room

la salono is not a direct object. It is part of a prepositional phrase with en, so it stays salono without -n.

This is about the difference between location and movement toward a place.

• en la salono = in the living room (location)
• en la salonon = into the living room (movement into it)

In the sentence, the children are already playing there, so Esperanto uses en la salono.

Dum means while here. It connects two actions happening at the same time:

• La infanoj ludas en la salono
• dum la patrino preparas supon

So the idea is that the children are playing while the mother is preparing soup.

Depending on context, dum can also relate to during, but in this sentence it functions like the conjunction while.

La is the definite article in Esperanto, meaning the.

So:

• la infanoj = the children
• la salono = the living room
• la patrino = the mother

A useful thing to remember: la never changes.

It does not matter whether the noun is:

• singular or plural
• subject or object
• masculine or feminine

It is always just la.

Esperanto has a definite article, la, but it does not have an indefinite article like English a or an.

So:

• supo can mean soup, a soup, or sometimes some soup, depending on context
• supon is that same noun in the direct-object form

That is why Esperanto simply says preparas supon, not something like preparas a soup.

Because Esperanto often builds words from smaller parts.

• patro = father / parent in the basic family-word set
• -in- = female suffix
• patrino = mother

So patrino is formed from patro + -in- + -o.

This word-building system is very common in Esperanto and helps make vocabulary more predictable.

Esperanto word order is more flexible than English, because endings show grammatical roles.

The normal, neutral order here is:

• La infanoj ludas en la salono dum la patrino preparas supon.

That is a very natural order. But some rearranging is possible for style or emphasis.

For example, you could also say:

• Dum la patrino preparas supon, la infanoj ludas en la salono.

That means essentially the same thing, but it starts with the while clause.

Not necessarily. In Esperanto, punctuation is somewhat flexible, especially with short subordinate clauses.

So both of these can be acceptable depending on style:

• La infanoj ludas en la salono dum la patrino preparas supon.
• La infanoj ludas en la salono, dum la patrino preparas supon.

Many writers would omit the comma in a short sentence like this, as in your example.

You identify the subject by meaning and structure, and sometimes by endings.

In the first part:

• La infanoj ludas
  The children are the ones doing the playing, so la infanoj is the subject.

In the second part:

• la patrino preparas supon
  The mother is doing the preparing, so la patrino is the subject.

And supon has -n, which shows it is the direct object, not the subject.

So the endings help make the sentence clear.

Infanoj means children, and it is not limited to boys. It can include boys, girls, or a mixed group.

The singular is:

• infano = child

The plural is:

• infanoj = children

So it is a general word, just like English children.