Cum aestas venisset, parentes pueros ad litus duxerunt, et pueri in arena diu luserunt.

Here cum means when.

More specifically, it introduces a clause that gives the background situation for the main action:

• Cum aestas venisset = when summer had come / when summer arrived

In Latin, cum can also mean since or although in other sentences, so learners often need to decide from the context which sense fits.

Because after cum, Latin often uses the subjunctive when the clause gives the circumstances/background of the main action.

So in this sentence:

• Cum aestas venisset does not just give a bare clock-time fact
• it sets the scene for what happened next

This is a very common construction in Latin narrative, often called a cum clause.

Venisset is pluperfect subjunctive active, from venio, venire.

It is pluperfect because the coming of summer happened before the two main actions:

• first, summer came
• then, the parents took the boys to the shore
• then, the boys played in the sand

So Latin uses the pluperfect to show that this action was already completed before the main events.

Venisset breaks down as:

• verb: venio, venire = to come
• tense: pluperfect
• mood: subjunctive
• voice: active
• person: 3rd
• number: singular

So it means had come.

It is singular because its subject, aestas, is singular.

Aestas is nominative singular.

It is nominative because it is the subject of venisset:

• aestas venisset = summer had come

Its dictionary form is also aestas, so here the nominative singular looks like the basic form you would find in a vocabulary list.

Because they have different jobs in the sentence.

• parentes = the parents → subject of duxerunt
• pueros = the boys → direct object of duxerunt

So:

• parentes is nominative plural
• pueros is accusative plural

Latin uses case endings to show who is doing the action and who is receiving it.

Because in the second clause the boys are no longer the object; they become the subject.

Compare:

• parentes pueros ad litus duxerunt
  The parents took the boys to the shore.
  Here pueros is the object.

• et pueri in arena diu luserunt
  And the boys played in the sand for a long time.
  Here pueri is the subject.

So the form changes because the grammatical role changes:

• pueros = accusative plural
• pueri = nominative plural

Because the two prepositions work differently here.

• ad
  • accusative usually shows motion toward
• in
  • ablative usually shows location where something happens

So:

• ad litus = to the shore
• in arena = in/on the sand

This is a very important Latin pattern:

• ad answers to where?
• in with the ablative answers where?

Good question. Litus is a neuter third-declension noun, and in many neuter nouns the nominative and accusative singular are the same.

So:

• nominative singular: litus
• accusative singular: litus

That is why after ad you still see litus, even though it is accusative.

Because in is being used to mean in/on, expressing location, and with that meaning it takes the ablative.

So:

• arena here is ablative singular
• the basic noun is arena, arenae

If Latin wanted to say into the sand, with motion into something, you would normally expect in + accusative instead.

Both are perfect indicative active, 3rd person plural.

• duxerunt = they led / they took
• luserunt = they played

They are plural because their subjects are plural:

• parentes duxerunt
• pueri luserunt

The perfect presents these actions as completed events in the storyline:

• the parents took the boys to the shore
• the boys played for a long time

This moves the narrative forward.

If Latin used the imperfect, it would sound more like ongoing background action, for example were taking or were playing. Here the perfect is natural because the sentence tells a sequence of events.

Yes, literally they led, from duco, ducere.

But in context it is often best understood as took or brought:

• parentes pueros ad litus duxerunt = the parents took the boys to the shore

Latin often uses duco where English would prefer take when someone leads people somewhere.

It comes from ludo, ludere, meaning to play.

So:

• luserunt = they played

This is a good verb to remember because its perfect stem changes:

• present: ludo
• perfect: lusi
• so 3rd plural perfect: luserunt

Diu is an adverb, meaning for a long time or a long while.

It modifies luserunt:

• pueri in arena diu luserunt = the boys played in the sand for a long time

Because it is an adverb, it does not change its form to agree with any noun.

Latin often leaves out subject pronouns, but it can still repeat a noun for clarity, contrast, or simply a natural narrative style.

Here the repetition helps mark the shift from:

• the parents doing the action in the first clause

to

• the boys doing the action in the second clause

So repeating pueri makes the sentence very clear and smooth.