Il bambino vede un alieno.

Il is the masculine singular definite article, meaning the.

So il bambino means the child/the boy.

In Italian, articles are used very often, often more than in English. A bare noun like bambino is possible in some contexts, but in a basic sentence like this, il bambino is the normal way to say the child.

It can mean either, depending on context.

• bambino = a male child, so often boy
• more generally, it can also be understood as child

Its feminine form is bambina, meaning girl or female child.

So grammatically, bambino is masculine singular.

Vede is the third-person singular present tense of the verb vedere (to see).

So:

• vedere = to see
• vede = he/she sees or it sees

In this sentence, the subject is il bambino, so vede means the child sees.

A few present-tense forms of vedere are:

• io vedo = I see
• tu vedi = you see
• lui/lei vede = he/she sees
• noi vediamo = we see
• voi vedete = you all see
• loro vedono = they see

Because alieno is a masculine singular noun beginning with a vowel, and the correct indefinite article here is un.

For masculine nouns:

• un is used before most nouns, including many nouns starting with a vowel
• uno is used before certain special sound combinations, such as:
  • z: uno zaino
  • s + consonant: uno studente
  • gn: uno gnomo
  • ps: uno psicologo
  • x: uno xilofono

So:

• un alieno = correct
• uno alieno = not correct

Also, notice that un here has no apostrophe.

Because Italian usually does not need subject pronouns when the subject is already clear.

In English, you must say He sees or The child sees.

In Italian, the verb ending often already tells you the person, and here the noun il bambino is explicitly stated anyway. So there is no need to add lui.

• Il bambino vede un alieno. = The child sees an alien.
• Lui vede un alieno. = He sees an alien.

Adding lui is possible, but it usually adds emphasis or contrast.

Yes. This sentence uses the most common Italian word order:

subject + verb + object

• Il bambino = subject
• vede = verb
• un alieno = object

So:

Il bambino vede un alieno. = The child sees an alien.

If you change the order, the meaning may change or the sentence may sound marked or unusual. For example:

• Un alieno vede il bambino. = An alien sees the child.

That is a different meaning, because now un alieno is the subject.

Yes. Alieno can be both a noun and an adjective.

In this sentence, it is a noun:

• un alieno = an alien

But as an adjective, alieno can mean something like foreign, unrelated, or strange depending on context.

For example:

• un mondo alieno = an alien/foreign world

Here, though, because it comes after un and stands alone as a thing/person being seen, it clearly functions as a noun.

A simple pronunciation guide is:

eel bam-BEE-no VEH-deh oon ah-LYEH-no

A few notes:

• il sounds roughly like eel
• bambino has stress on -bi-: bam-BEE-no
• vede has stress on ve-: VEH-deh
• alieno has stress on -e-: a-LYEH-no

The vowels are usually pronounced clearly in Italian, and each syllable is heard more distinctly than in English.

Very often, yes.

Italian uses articles more regularly than English does. In a sentence like this, both articles are natural and expected:

• il bambino = the child
• un alieno = an alien

Leaving them out would usually sound incomplete or unnatural in standard Italian.

So this sentence is a good example of normal article use: Il bambino vede un alieno.

Yes.

Because bambino can mean boy or child, the sentence can naturally be understood as either:

• The child sees an alien
• The boy sees an alien

The exact English translation depends on context. If the speaker wants to make it clearly feminine, Italian would use bambina instead.