Pater vetat filium sero extra domum manere.

Because filium is the person being forbidden, and with vetat Latin commonly uses an accusative + infinitive pattern:

• pater = the subject of vetat
• filium = the person whom the father forbids
• manere = what that person is forbidden to do

So filium is not the direct object in the same way as in a simple English sentence; it is also the understood subject of the infinitive manere.

After vetat (forbids), Latin often uses an infinitive to express the action that is being forbidden.

So:

• vetat = he forbids
• manere = to stay / to remain

This is very natural Latin. English can do something similar with forbids his son to stay.

The subject of manere is filium.

Even though filium is accusative, it is still the one doing the staying. In other words:

• pater vetat = the father forbids
• filium manere = the son to stay

This is a common Latin construction: the subject of the infinitive is put in the accusative.

Because pater is the nominative singular form of the noun pater, patris (father).

Not all nominative singular nouns end in -us or -a. Pater belongs to the third declension, and its nominative form is simply pater.

Here it is nominative because it is the subject of vetat.

Sero is an adverb meaning late.

It modifies manere, so it tells us when the staying happens:

• manere = to stay
• sero manere = to stay late

It does not describe the father or the son; it describes the action.

Because extra is a preposition that takes the accusative.

So:

• extra = outside
• domum = accusative singular of domus

Together, extra domum means outside the house.

This is different from the special adverbial use of domum by itself meaning homeward. In this sentence, domum is simply the object of extra.

Extra domum is a prepositional phrase, and it belongs with manere.

So the structure is:

• filium ... manere = the son to stay
• sero = late
• extra domum = outside the house

All three of those complete the idea of manere.

Classical Latin does not have articles like English the or a/an.

So pater can mean:

• father
• the father
• sometimes even a father

and filium can mean:

• son
• the son
• sometimes a son

The correct English article is chosen from context.

Good question. Strictly speaking, Latin here only says father and son. It does not explicitly say his son.

If Latin wanted to make that explicit, it could use suum:

• Pater vetat suum filium... = The father forbids his own son...

In many contexts, English naturally says his son because that is the most likely relationship, but the Latin sentence itself does not force that meaning unless context does.

Yes, the word order is normal, but Latin is much freer than English.

This sentence puts:

• pater first
• vetat early
• manere at the end

That is a very common Latin pattern. But Latin could rearrange the words for emphasis without changing the basic meaning, as long as the forms stay the same.

For example, Pater filium extra domum sero manere vetat would mean essentially the same thing.

Because manere means to stay or to remain, not to go.

So the idea is not that the son is forbidden to go outside, but that he is forbidden to stay outside.

That distinction matters:

• extra domum manere = to remain outside the house
• extra domum ire = to go outside the house

Latin is being precise about the action.

Yes. Latin adverbs are fairly flexible in position.

For example:

• Pater vetat filium sero extra domum manere
• Pater vetat filium extra domum manere sero

Both are understandable, though the first is more natural and better balanced.

Latin often places adverbs where they are most useful for emphasis or rhythm, not according to a rigid rule like English.

The main finite verb is vetat.

That is the verb that tells you what the sentence is asserting:

• pater vetat = the father forbids

Everything else helps complete that statement:

• filium = whom he forbids
• manere = what he forbids him to do
• sero extra domum = the circumstances of that action