Дети шепчутся в комнате, когда мама спит.

The verb here is шептаться, not шептать.

• шептать = to whisper something
• шептаться = to whisper among themselves / to whisper to each other

So -ся often gives the verb a reflexive or reciprocal sense. In this sentence, Дети шепчутся means the children are whispering to each other, not just whispering words in general.

Шепчутся is the correct 3rd person plural present form of шептаться.

Its present-tense forms are:

• я шепчусь
• ты шепчешься
• он/она шепчется
• мы шепчемся
• вы шепчетесь
• они шепчутся

The stem changes from шепт- to шепч- in these forms. That kind of consonant change is normal in Russian conjugation and just has to be learned as part of the verb.

Дети is the nominative plural form, because it is the subject of the sentence.

The singular is:

• ребёнок = child

But the plural is irregular:

• дети = children

So Дети шепчутся means the children are whispering.

Because this sentence describes location, not movement.

After в:

• в комнате = in the room → location, so prepositional case
• в комнату = into the room → direction/motion, so accusative case

Here the children are already whispering in the room, so в комнате is correct.

Комнате is the prepositional singular form of комната.

The pattern is:

• комната → nominative singular
• в комнате → prepositional singular

This is very common after prepositions like в, на, о, when talking about location or topic.

It can mean any of those, depending on context.

Спит is the 3rd person singular present of спать. Russian present tense often covers both:

• simple present: sleeps
• present continuous: is sleeping

And in English, with this kind of sentence, you might also translate it as is asleep.

So this sentence could be understood as:

• The children whisper in the room when Mom sleeps
• The children are whispering in the room while Mom is sleeping
• The children whisper in the room when Mom is asleep

The exact English wording depends on context.

Grammatically, когда means when, but in context it can often be translated as while.

Here the two actions happen at the same time:

• the children whisper
• Mom sleeps

So English often prefers while for naturalness: while Mom is sleeping.

Russian still uses когда in many cases where English might choose either when or while.

Because the sentence describes an ongoing or habitual situation, not a completed event.

• шепчутся is imperfective
• спит is imperfective

Imperfective verbs are used for:

• ongoing actions
• repeated actions
• background situations

That fits this sentence well.

Also, in Russian, a perfective present usually has future meaning, not true present meaning. So a perfective verb would not normally work here if you want to say what is happening now or usually happens.

Yes. The comma is required because когда мама спит is a subordinate clause.

Russian normally separates a main clause and a subordinate clause with a comma:

• Дети шепчутся в комнате, когда мама спит.
• Когда мама спит, дети шепчутся в комнате.

So the comma is correct no matter which clause comes first.

Yes. Russian word order is fairly flexible.

The original sentence is a neutral, natural order:

• Дети шепчутся в комнате, когда мама спит.

But you could also say:

• Когда мама спит, дети шепчутся в комнате.
• Дети в комнате шепчутся, когда мама спит.

The basic meaning stays the same, but the emphasis changes. Russian often uses word order to highlight what is most important or most new in the sentence.

Because Russian has no articles.

So Russian usually just says:

• дети = children / the children
• комната = room / the room / a room
• мама = Mom / the mother

English has to choose a or the, but Russian leaves that to context.

The stress is:

• Де́ти ше́пчутся в ко́мнате, когда́ ма́ма спит.

A few useful notes:

• Де́ти = stress on the first syllable
• ше́пчутся = stress on ше́-
• ко́мнате = stress on ко́м-
• когда́ = stress on the last syllable
• ма́ма = stress on the first syllable
• спит = one syllable, so it is stressed

Also, the ending -тся in шепчутся is usually pronounced roughly like -ца in normal speech.