Learn Hardcore Greek: Το παιδί που μιλάει με πολλούς ανθρώπους είναι εδώ. - The child who talks with many people is here.

Here που is the invariable relative pronoun meaning who/that/which: το παιδί που μιλάει... = the child who/that speaks...
It is not the same as πού (with an accent), which means where? as a question word.
Pronunciation is the same [pu], but the accent mark changes the meaning in writing. Only πού takes the accent.

Why is it μιλάει? Could I also say μιλά?

Both are correct 3rd person singular present of μιλάω/μιλώ (to speak).
Forms: εγώ μιλάω/μιλώ, εσύ μιλάς, αυτός/αυτή/αυτό μιλά(ει).
μιλάει is more common in casual writing/spelling, μιλά is a shorter form often seen in written standard Greek. They are interchangeable in meaning.
Pronunciation: μιλάει may be pronounced as two syllables [mi-LA-i] or contracted to [mi-LA]; μιλά is [mi-LA].

Why μιλάει με here? Can I use μιλάει σε, or no preposition?

With people, Greek typically uses:
- μιλάω με κάποιον = talk with someone (mutual interaction)
- μιλάω σε κάποιον = talk to someone (one-direction emphasis)
Both are common and correct; nuance is similar to English with/ to.
No preposition when the object is a language: μιλάει ελληνικά = he/she speaks Greek.

What case is πολλούς ανθρώπους, and why those endings?

ανθρώπους is accusative plural masculine of άνθρωπος (person).
πολλούς is the accusative plural masculine of πολύς (many), agreeing with ανθρώπους in gender/number/case.
The preposition με always takes the accusative, hence με πολλούς ανθρώπους.

Why is Το παιδί neuter? Does that tell us the child’s gender?

παιδί is grammatically neuter and means child irrespective of gender; it does not tell you whether it’s a boy or a girl.
If you want to specify: το αγόρι (boy), το κορίτσι (girl). The sentence structure otherwise stays the same.

Should there be a comma before που?

No comma for a restrictive clause (it identifies which child): Το παιδί που μιλάει...
Commas mark a non‑restrictive aside: Το παιδί, που μιλάει με πολλούς ανθρώπους, είναι εδώ = The child, who (by the way) talks with many people, is here. This changes the nuance.

Can I say Εδώ είναι instead of είναι εδώ?

How do I pronounce the sentence?

Rough IPA: [to peˈði pu miˈla(i) me poˈlus anˈθropus ˈine eˈðo]
Simple guide: to pe-DHI pu mi-LA(i) me po-LOOS an-THRO-pus EE-ne e-THO
Tips:
- θ = th in English think; δ = th in this.
- ου = oo (as in food).
- μιλάει can be [mi-LA-i] or contracted to [mi-LA].

Does που change form to agree with παιδί? Could I use ο οποίος/η οποία/το οποίο?

που is invariable: it does not change for gender, number, or case.
A more formal alternative is the agreeing relative pronoun ο/η/το οποίος/α/ο. Here: Το παιδί το οποίο μιλάει με πολλούς ανθρώπους είναι εδώ (more formal/literary style).

Why is the verb inside the relative clause singular (μιλάει)?

The understood subject of the relative clause is the head noun το παιδί (singular), so the verb is 3rd person singular.
If it were plural: Τα παιδιά που μιλάνε/μιλούν με πολλούς ανθρώπους είναι εδώ.

Can I drop the article Το?

Not if you mean a specific, definite child. Greek typically uses the definite article where English uses “the.”
To be indefinite, use Ένα παιδί (a child): Ένα παιδί που μιλάει με πολλούς ανθρώπους είναι εδώ.

What’s the difference between μιλάω/μιλώ and λέω?

μιλάω/μιλώ = speak/talk (general act of speaking): Μιλάει με πολλούς ανθρώπους = He/She talks with many people.
λέω = say/tell (the content): Λέει πολλά = He/She says a lot; Του λέει την αλήθεια = She tells him the truth.

Can I use another word instead of ανθρώπους, like κόσμο or άτομα?

Yes, with nuance:
- κόσμο (acc. sg.) often means “people” collectively: μιλάει με πολύ κόσμο = talks with lots of people (colloquial).
- άτομα (individuals) is more neutral/administrative: μιλάει με πολλά άτομα. It can feel impersonal in some contexts.
- ανθρώπους is the most straightforward “people/persons.”

How would I say “The child I’m talking with is here”?

When the child is the person you are talking with (object of the preposition), use:
- Το παιδί που μιλάω μαζί του είναι εδώ. (common, with resumptive pronoun)
- More formal: Το παιδί με το οποίο μιλάω είναι εδώ.
Note: You cannot “strand” the preposition in Greek; you either use μαζί του/της or με το οποίο.

Why not Το παιδί που μιλάει πολλούς ανθρώπους (without με)?

Because μιλάω does not take a direct object for the person you speak with; it needs a preposition (με = with, or σε = to). Without a preposition, it’s ungrammatical in this meaning.

Is είναι εδώ different from βρίσκεται εδώ?

είναι εδώ = is here (neutral, the default).
βρίσκεται εδώ = is located/found here (more formal or locative; fine for places or formal contexts, a bit stiff for everyday speech about a person).

When do I use πολύ vs πολλοί/πολλές/πολλά?

πολύ is an adverb (very/much) or neuter singular for uncountable nouns: πολύ νερό (much water).
πολλοί/πολλές/πολλά are adjective forms for countable plurals: πολλοί άνθρωποι (many people), πολλές μέρες (many days), πολλά παιδιά (many children).
Here we need masculine accusative plural: πολλούς ανθρώπους.