Quia puer cecidit, parvum vulnus in genu habet, et paene nullus sanguis est.

Quia means because. It introduces a clause that gives the reason for something.

So in this sentence:

Quia puer cecidit = Because the boy fell

That whole clause explains why the boy now has a wound and almost no blood. Latin often puts this kind of reason clause first, just as English can.

Puer is nominative singular. It is the subject of cecidit:

• puer = the boy
• cecidit = fell

So puer cecidit means the boy fell.

It is also useful to notice that puer is a second-declension masculine noun, but unlike many others it ends in -er rather than -us.

Cecidit is perfect tense: he fell.

Latin uses the perfect here because the fall is a completed action. The boy already fell, and now there is a present result:

• he has a small wound
• there is almost no blood

So the sentence moves naturally from a past event to the boy’s present condition.

Because cecidit is the perfect form of cado, cadere (to fall), and this verb has an irregular-looking perfect stem.

Its principal parts are:

• cado
• cadere
• cecidi
• casum

From cecidi we get cecidit = he/she/it fell.

This is a good reminder that in Latin you often need to learn a verb’s principal parts, because the perfect stem may not be obvious from the present stem.

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

So:

• puer can mean the boy or a boy
• parvum vulnus can mean a small wound or the small wound, depending on context

The translator supplies the or a based on what sounds natural in English.

Because parvum agrees with vulnus.

Vulnus is:

• neuter
• singular
• accusative

So the adjective must also be:

• neuter
• singular
• accusative

That gives parvum.

If the noun were masculine nominative singular, then you might get parvus instead.

Vulnus is accusative singular because it is the direct object of habet:

• habet = he has
• what does he have? parvum vulnus

A detail that often confuses learners: vulnus is a third-declension neuter noun, and in neuter nouns the nominative and accusative singular are often the same form. So even though it is accusative here, it still appears as vulnus.

Here in genu means the wound is located on/in the knee, and natural English usually says on the knee.

The important grammar point is this:

• in + ablative = location: in/on/at
• in + accusative = motion into/onto

Since the wound is already located there, Latin uses in genu with the ablative.

Also, genu is a somewhat unusual noun: it is a fourth-declension neuter noun meaning knee.

Latin often leaves out possessive words like his, her, or their when the owner is obvious from the context, especially with body parts.

So in genu habet naturally means he has [it] on his knee.

Latin could say in suo genu for on his own knee, but that would usually be more explicit or emphatic than necessary.

This part literally means almost no blood is.

A few things are happening here:

• paene = almost
• nullus = no, not any
• sanguis = blood
• est = is

So nullus sanguis is the subject of est, which is why it is in the nominative, not the accusative.

Also, Latin often uses est without a separate word for English there. So:

• paene nullus sanguis est
  = there is almost no blood

And sanguis is singular because blood is treated as a mass noun.

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

This sentence uses a very natural order:

• reason first: Quia puer cecidit
• then the present result: parvum vulnus in genu habet
• then an added statement: et paene nullus sanguis est

The verbs also appear near the ends of their clauses, which is very common in Latin.

You could rearrange some of the words and still keep the same basic meaning, but the chosen order is smooth and straightforward.