Mater respondet se paucos nummos habere, sed argentum mox mutare velle.

Because Latin is using an indirect statement after respondet.

In English, we would often say something like Mother replies that she has.... In Latin, instead of that she has, the language usually uses:

• an accusative subject
• plus an infinitive verb

So:

• se = herself / she in the accusative
• habere = to have

Together, se ... habere means that she has ...

Also, se is reflexive, so it refers back to the subject of the main verb, which is mater.

For the same reason: this is the standard Latin construction for reported speech / indirect statement.

After a verb like respondet (she answers / replies), Latin often does not use a clause with that. Instead it uses the accusative-and-infinitive construction:

• se paucos nummos habere = that she has few coins
• (se) argentum mox mutare velle = that she wants to change money soon

So the infinitives are not random; they are required by the construction.

Because the subject is the same, and Latin often leaves it understood.

The full sense is:

• Mater respondet se paucos nummos habere, sed (se) argentum mox mutare velle.

The second se is unnecessary because once Latin has already made the subject clear, it can omit it in the next coordinated infinitive phrase.

So the sentence means:

• Mother replies that she has few coins, but wants to change money soon.

Both words are accusative plural.

• nummos is the direct object of habere
• paucos agrees with nummos in case, number, and gender

So:

• nummos = coins
• paucos nummos = few coins

Even though se is also accusative, it has a different job:

• se = subject of the infinitive habere
• paucos nummos = object of habere

That is a very common pattern in Latin indirect statement.

Normally paucos means few, not many, or only a small number of.

So paucos nummos habere suggests that she does not have many coins.

A learner should notice that this is not the same as just saying some coins. It usually carries the idea of scarcity.

Literally, argentum means silver.

But like many money-words in Latin, it can also mean silver money, cash, or money more generally, depending on context.

So in this sentence, argentum mox mutare most likely means something like:

• to change money soon
• to exchange some money soon

The exact English wording depends on the context you were given, but the important point is that argentum does not always mean only the metal itself.

Velle is the present active infinitive of volo, which means I want.

Its principal parts are:

• volo
• velle
• volui

It is an irregular verb, so the infinitive is velle, not something regular like volare or amare.

Here it means to want, and it depends on respondet as part of the indirect statement.

Sed means but.

It connects two parts of the reported statement:

• se paucos nummos habere
• (se) argentum mox mutare velle

So the mother is replying with two linked ideas:

1. she has few coins
2. but she wants to change money soon

Everything after respondet is still part of what she says.

Latin word order is more flexible than English word order.

Here mox (soon) is placed right before mutare to go naturally with that action:

• argentum mox mutare
• to change money soon

Latin often puts adverbs near the word they modify, but not always. You could find a different word order in another sentence without changing the basic grammar.

Because Latin usually does not need a separate word for that in this kind of construction.

English says:

• She replies that she has few coins.

Latin usually says:

• She replies herself few coins to have
• that is, respondet se paucos nummos habere

This may feel strange to an English speaker at first, but it is one of the most important Latin patterns to learn.

Yes. If Latin wants to say who she replies to, it can add that person, usually in the dative:

• mater puero respondet = mother replies to the boy

In your sentence, that person is simply not expressed. Latin leaves it out when the context already makes it clear or when it is not important.

Not in a way that changes the basic meaning.

The order:

• Mater respondet
• se paucos nummos habere
• sed argentum mox mutare velle

is a natural Latin arrangement:

• main clause first
• then the reported content
• with the infinitives often placed toward the end of their phrases

A different order could still be grammatical, but this one is straightforward and idiomatic.