Antaŭ la vojaĝo la patrino kisis sian filon.

Esperanto word order is quite flexible. Starting with Antaŭ la vojaĝo puts the time expression first, like Before the trip, ... in English.

So:

• Antaŭ la vojaĝo la patrino kisis sian filon. = Before the trip, the mother kissed her son.

You could also say:

• La patrino kisis sian filon antaŭ la vojaĝo.

Both are correct. The first version emphasizes the time more.

Antaŭ means before.

In this sentence it is a preposition introducing a time phrase:

• antaŭ la vojaĝo = before the trip

Because antaŭ is a preposition, the noun after it normally does not take -n just because it follows the preposition. That is why we get:

• la vojaĝo, not la vojaĝon

La is the definite article, meaning the.

So:

• vojaĝo = a trip / trip
• la vojaĝo = the trip

Esperanto uses la when the speaker and listener are thinking of a specific thing. In this sentence, it is a particular trip, so la vojaĝo is natural.

Kisis comes from the verb kisi, meaning to kiss.

Esperanto verb endings show tense very regularly:

• -as = present
• -is = past
• -os = future

So:

• kisas = kisses / is kissing
• kisis = kissed
• kisos = will kiss

That makes la patrino kisis mean the mother kissed.

The -n ending marks the direct object in Esperanto.

Here, la patrino is the one doing the action, and sian filon is the one receiving the action of kissing. So:

• la patrino = subject
• sian filon = direct object

That is why filo becomes filon.

This is a very common question.

Sia is the reflexive possessive pronoun. It means something like his/her/their own, but it refers back to the subject of the clause.

In this sentence, the subject is la patrino, so:

• sian filon = her own son

If you said ŝian filon, that would usually mean her son, but belonging to some other female person, not the subject.

So:

• La patrino kisis sian filon. = The mother kissed her own son.
• La patrino kisis ŝian filon. = The mother kissed her son, where her refers to another woman.

Yes, within its own clause, sia refers back to the subject of that clause.

In this sentence:

• subject = la patrino
• therefore sian filon refers to the mother’s son

This rule helps avoid ambiguity. English her can be unclear, but Esperanto distinguishes clearly between:

• sia = the subject’s own
• ŝia = some female person’s, not the subject

Because sian agrees with filon, which is in the accusative.

The possessive adjective must match the noun it goes with in number and case:

• sia filo = her own son
• sian filon = her own son, as direct object

Here filon has -n, so sian also takes -n.

La patrino means the mother.

Esperanto has only one article, la, for the. There is no separate word for a/an.

So:

• patrino = mother / a mother
• la patrino = the mother

In this sentence, we are talking about a specific mother, so la patrino is used.

Yes. Because Esperanto marks the direct object with -n, word order is freer than in English.

For example, these are all possible:

• Antaŭ la vojaĝo la patrino kisis sian filon.
• La patrino kisis sian filon antaŭ la vojaĝo.
• Sian filon la patrino kisis antaŭ la vojaĝo.

They all mean basically the same thing, but the emphasis changes. The original sentence emphasizes the time first.

Yes.

• filo = son
• filino = daughter
• infano = child

So sian filon specifically means her own son.

Then you would not use sia.

For example:

• Antaŭ la vojaĝo la patrino kisis ŝian filon.
  = Before the trip the mother kissed her son.
  Here ŝian refers to another female person.

Or:

• Antaŭ la vojaĝo la patrino kisis lian filon.
  = Before the trip the mother kissed his son.

So sia is used only when the possession belongs to the subject.