Μιλάμε χαμηλόφωνα όταν το παιδί κοιμάται.

In Greek, the verb ending often already tells you who the subject is.
Μιλάμε means we speak / we are speaking, so a separate pronoun like εμείς is usually unnecessary.

You could say Εμείς μιλάμε χαμηλόφωνα..., but that would normally add emphasis, as if you were stressing we.

Μιλάμε is the 1st person plural, present tense form of μιλάω / μιλώ (to speak / talk).

So it means:

• we speak
• we are speaking
• sometimes we talk

In this sentence, it has a general/habitual sense:
We speak quietly when the child is sleeping / whenever the child sleeps.

χαμηλόφωνα is an adverb, and it means:

• quietly
• softly
• literally something like in a low voice

It comes from χαμηλόφωνος (low-voiced / soft-spoken), but here the adverb form is used.

So:

• Μιλάμε χαμηλόφωνα = We speak quietly / in a low voice

A learner might expect something like χαμηλά, but χαμηλόφωνα is more natural when talking specifically about speaking in a quiet voice.

όταν means when, but in many sentences like this one it can also have the sense of whenever.

Here the sentence expresses a repeated/general situation, not just one single event, so English could understand it as:

• when the child is sleeping
• whenever the child sleeps

Both ideas fit the Greek sentence.

Because παιδί is a neuter noun in Greek.

Greek nouns have grammatical gender, and παιδί takes the neuter article:

• το παιδί = the child

So even if the child is a boy or a girl in real life, the noun παιδί is grammatically neuter.

In this sentence, το παιδί is the subject of κοιμάται, so it is in the nominative case.

For many neuter nouns, especially in the singular, the nominative and accusative forms are the same:

• nominative: το παιδί
• accusative: το παιδί

So even though Greek has cases, here there is no visible change.

κοιμάται is the 3rd person singular, present tense form of κοιμάμαι (to sleep).

So it means:

• he/she/it sleeps
• is sleeping

With το παιδί, it means:

• the child sleeps
• the child is sleeping

A useful thing to notice is that κοιμάμαι has the kind of form Greek learners often call middle/passive in appearance, but its meaning here is active: sleep.

Greek often uses the present tense for habitual or general situations, just as English does.

So this sentence is not necessarily about one specific moment only. It describes what usually happens:

• We speak quietly when the child is sleeping.

If you wanted a more clearly one-time past situation, Greek would normally use past forms instead.

Yes. Greek word order is fairly flexible.

The original sentence is:

• Μιλάμε χαμηλόφωνα όταν το παιδί κοιμάται.

But you could also say:

• Όταν το παιδί κοιμάται, μιλάμε χαμηλόφωνα.

This version puts the when-clause first and may sound a little more natural in some contexts.

The basic meaning stays the same. Word order changes usually affect focus or emphasis, not the core meaning.

Here it is an adverb, because it describes how we speak.

• μιλάμε = verb
• χαμηλόφωνα = tells us the manner of speaking

So it answers the question How do we speak?
Answer: χαμηλόφωνα = quietly / softly

A rough pronunciation guide is:

Mi-LA-me ha-mi-LO-fo-na O-tan to pe-THI ki-MA-te

A few helpful notes:

• Μιλάμε has the stress on λά
• χαμηλόφωνα has the stress on λό
• παιδί has the stress on the last syllable: -δί
• κοιμάται has the stress on μά

Also, δ in Modern Greek is pronounced like th in this, so παιδί sounds roughly like pe-THEE.

Yes. The Greek present tense can cover both:

• We speak quietly
• We are speaking quietly

Which one sounds best in English depends on context.

In this sentence, because of όταν το παιδί κοιμάται, the most natural interpretation is usually habitual/general:

• We speak quietly when the child is asleep / sleeping.

But grammatically, the Greek present is broad enough to overlap with both English simple present and present progressive in different contexts.