Quamvis puer timidus sit, tamen matri supplicat et dicit fas esse culpam aperte fateri.

Because quamvis normally introduces a concessive clause with the subjunctive in classical Latin.

So:

• quamvis ... sit = although ... is
• not because the writer is unsure, but because this is the standard grammar after quamvis

The tense is present subjunctive because the boy’s being timid is happening at the same time as the main action.

They form a very common pair in Latin:

• quamvis = although
• tamen = nevertheless / still / yet

So Latin often says, in effect:

• Although X, nevertheless Y

English can do the same, but often drops nevertheless. Latin likes the pairing because it makes the contrast very clear.

Because timidus is a predicate adjective describing puer.

In puer timidus sit:

• puer = the boy
• timidus = timid
• sit = is

Since timidus refers back to puer, it must agree with it in:

• case: nominative
• number: singular
• gender: masculine

So timidus is not an adverb or separate noun; it is simply the adjective linked to puer by sit.

Yes.

Latin often states the subject once and then continues with more verbs referring to the same subject unless something changes.

So here the understood structure is:

• puer ... supplicat
• puer ... dicit

The boy is the one who:

• is timid
• begs his mother
• says that confessing fault openly is right

Because supplicare commonly takes the dative of the person appealed to.

So:

• matri supplicat = he begs/pleads to his mother

This is different from English, where we usually use a preposition such as to. Latin often expresses that idea just by the dative ending.

Supplicat comes from supplicare, which means something like:

• to beg
• to plead
• to implore
• to appeal humbly

It has a strong sense of humility or earnest appeal. So it is stronger and more emotional than a simple he asks.

This is the content of what he says.

After verbs like dicit, Latin often reports speech with an infinitive construction instead of using that the way English does.

So the basic idea is:

• dicit = he says
• fas esse culpam aperte fateri = that it is right to confess fault openly

The whole infinitive phrase functions as the thing being said.

fas est is an impersonal expression meaning:

• it is right
• it is permitted
• it is morally or religiously proper

So fas esse means to be right / to be permitted in indirect statement.

A useful point: fas is a special indeclinable word. It does not change its form like an ordinary noun.

Because it depends on dicit.

After he says, Latin often uses an infinitive to express that ... is. So:

• dicit fas esse = he says that it is right

If this were a direct statement, it would be:

• fas est = it is right

But after dicit, est becomes esse.

Because it depends on fas esse.

The structure is:

• fas esse = that it is right
• culpam aperte fateri = to confess fault openly

So Latin is saying literally:

• he says it to be right to confess fault openly

More natural English:

• he says that it is right to confess fault openly

Because fateri is a deponent verb.

Deponent verbs:

• have passive-looking forms
• but active meanings

So:

• fateri looks passive in form
• but means to confess, not to be confessed

Its full dictionary form is fateor, fateri, fassus sum.

Because it is the direct object of fateri.

He is confessing what?

• culpam = fault / guilt / wrongdoing

So:

• culpam fateri = to confess a fault

Even though fateri is deponent, it can still take a direct object just like an active verb.

Aperte is an adverb, and it modifies fateri.

So it tells us how the confessing is done:

• aperte fateri = to confess openly

It does not modify culpam. It describes the action, not the noun.

Yes, but mostly in terms of emphasis rather than basic grammar.

Latin word order is flexible because the endings show the grammatical relationships. Here the order does a few useful things:

• Quamvis ... sit sets up the concession first
• tamen marks the turn to the main point
• matri comes before supplicat, giving some prominence to the person he appeals to
• culpam aperte fateri keeps the object and adverb close to the infinitive they belong with

So the order is natural and expressive, but the endings are what tell you the grammar.