Quand le bébé dort, nous chuchotons dans le couloir.

Because le bébé is third-person singular: he/she/it sleeps.

The verb is dormir (to sleep), and in the present tense:

• je dors
• tu dors
• il / elle / on dort
• nous dormons
• vous dormez
• ils / elles dorment

So le bébé dort means the baby sleeps / is sleeping.

Because nous means we, so the verb has to match we.

The verb is chuchoter (to whisper), and the present tense is:

• je chuchote
• tu chuchotes
• il / elle / on chuchote
• nous chuchotons
• vous chuchotez
• ils / elles chuchotent

So nous chuchotons = we whisper / we are whispering.

In French, the present tense often covers both:

• simple present: we whisper
• present continuous: we are whispering

So this sentence can naturally describe a general situation or what is happening right now.

Likewise:

• le bébé dort can mean the baby sleeps or the baby is sleeping
• nous chuchotons can mean we whisper or we are whispering

French usually does not need a separate form like English is sleeping or are whispering.

Quand means when.

It introduces a time clause:

• Quand le bébé dort = When the baby is sleeping / When the baby sleeps

Putting it at the beginning is very natural in French, just as in English:

• When the baby sleeps, we whisper in the hallway.

You could also reverse the order:

• Nous chuchotons dans le couloir quand le bébé dort.

Both are correct.

It is standard and very natural here because the sentence begins with a clause introduced by quand:

• Quand le bébé dort, nous chuchotons dans le couloir.

This works like English:

• When the baby sleeps, we whisper in the hallway.

If the quand clause comes second, French often does not use a comma:

• Nous chuchotons dans le couloir quand le bébé dort.

Because dans means in / inside, which fits hallway / corridor.

• dans le couloir = in the hallway

Au usually means to the / at the, but it is not the natural choice here.

So:

• dans la chambre = in the bedroom
• dans la cuisine = in the kitchen
• dans le couloir = in the hallway

French usually uses an article where English sometimes does too, and sometimes does not.

Here, le couloir means the hallway. In a home or building context, French normally includes the article:

• dans le couloir
• dans la cuisine
• dans la salle de bain

So even if English might sometimes say in hallway speech less formally, French needs the article here.

Yes, you could say:

• Lorsque le bébé dort, nous chuchotons dans le couloir.

Both quand and lorsque can mean when.

However:

• quand is more common in everyday speech
• lorsque is often a bit more formal or literary

For normal conversation, quand is usually the better choice.

Bébé is pronounced roughly bay-bay.

A few helpful points:

• both é sounds are the same
• the é is a closed e sound, like ay in say, but without turning it into a diphthong too strongly
• stress in French is not like English stress; the rhythm is smoother

So:

• bébé ≈ bay-bay

Chuchotons is pronounced roughly shoo-shoh-tohn.

Breakdown:

• chu sounds like shu
• cho sounds like sho
• tons has a nasal vowel, so it is not pronounced like English tons

Important detail:

• the final s is silent

So the whole word sounds approximately like:

• shu-sho-ton with a nasal ending

Because many final consonants in French are silent.

In dort, the final t is normally not pronounced:

• dort sounds roughly like dor

This is very common in French spelling:

• petit → final t usually silent
• nez → final z silent
• parlent → final ent silent

So you have to learn pronunciation along with spelling.

Yes. In everyday spoken French, people very often use on instead of nous for we.

So you could hear:

• Quand le bébé dort, on chuchote dans le couloir.

That means the same thing as:

• Quand le bébé dort, nous chuchotons dans le couloir.

Difference:

• nous chuchotons is a bit more formal or careful
• on chuchote is very common in speech

It can mean either, depending on context.

It may describe:

• a general rule / habit: When the baby sleeps, we whisper in the hallway
• a current situation: When the baby is sleeping, we whisper in the hallway

French present tense often allows both interpretations, and the surrounding context tells you which one is meant.

French normally requires an explicit subject before each finite verb.

So you say:

• Quand le bébé dort, nous chuchotons...

Even though English also repeats the subject here, this is especially important in French. You generally cannot just leave out nous.

French verbs usually need a clear subject pronoun or noun:

• Je mange
• Tu parles
• Nous chuchotons

Usually, no important required liaison appears here in careful standard pronunciation.

For example:

• Quand le bébé dort: no standard liaison between quand and le
• bébé dort: no liaison
• nous chuchotons: no liaison
• dans le couloir: no liaison between dans and le

So the words are mostly pronounced separately.

That said, rhythm and linking in natural speech can still make the sentence flow smoothly, even without formal liaison.