Kada dete spava, televizor radi tiho.

Yes. Kada and kad both mean when.

• kada is the full form
• kad is a very common shorter form in everyday speech

So both of these are natural:

• Kada dete spava, televizor radi tiho.
• Kad dete spava, televizor radi tiho.

The version with kada may sound a little more neutral or careful.

The comma separates the subordinate time clause from the main clause.

• Kada dete spava = the time clause, telling us when
• televizor radi tiho = the main clause

In Serbian, when a subordinate clause comes first, a comma is normally used before the main clause.

Dete is in the nominative singular. It is the subject of spava.

So:

• dete = the child (subject)
• spava = sleeps / is sleeping

A native English speaker may expect some special marking, but here the basic dictionary form is used because it is the subject.

In Serbian, dete is a neuter noun. That is just how the word is classified grammatically.

Because it is neuter singular, adjectives and some past-tense forms would agree with it as neuter. For example:

• malo dete = a small child

Even though a real child is biologically male or female, the noun dete itself is grammatically neuter.

Because the subject dete is singular.

• dete spava = the child sleeps / is sleeping

Even though dete is neuter, the present-tense verb form is simply the normal 3rd person singular form. In the present tense, Serbian verbs do not show gender, only person and number.

Yes, literally radi often means works or is working, but with machines and appliances it often means:

• is on
• is operating
• is running

So televizor radi means the TV is on or operating, not that the TV has a job.

This is very natural Serbian usage for devices:

• Radio radi.
• Mašina radi.
• Televizor radi.

Because tiho is an adverb, and it modifies the verb radi.

• radi tiho = works quietly / is on quietly / plays at a low volume

If you used tih, that would be an adjective and would describe a noun, not the action. For example:

• televizor je tih = the TV is quiet

So in this sentence, tiho is correct because it describes how the TV is operating.

Usually it means the TV is on quietly, so the volume is low or at least not loud.

It describes the manner of operation, not just a permanent quality of the TV. In natural English, you would often understand it as:

• the TV is on quietly
• the TV is playing softly
• the TV is at low volume

Serbian often uses the present tense for actions that are:

• happening now
• habitual
• generally true in a repeated situation

So this sentence can mean something like:

• When the child is sleeping, the TV is on quietly or
• Whenever the child sleeps, the TV is on quietly

The exact interpretation depends on context. Serbian present tense is flexible in this kind of sentence.

Yes, often you can.

• kada = when
• dok = while

So:

• Dok dete spava, televizor radi tiho.

This sounds a bit more explicitly like while the child is sleeping.

A useful difference:

• kada can sound more like when/whenever
• dok emphasizes two actions happening at the same time

In many everyday situations, both are possible.

The word order is fairly flexible.

These are all possible, with slightly different emphasis:

• Kada dete spava, televizor radi tiho.
• Televizor radi tiho kada dete spava.
• Kada dete spava, tiho radi televizor. (less neutral, more marked)

The original version is the most neutral and natural for a learner to use.

Serbian does not have articles like English the and a/an.

So dete can mean:

• the child
• a child

and televizor can mean:

• the television
• a television

Context tells you which meaning is intended. In this sentence, English would usually translate it with the, but Serbian does not need to say that explicitly.

Exactly.

This sentence has two clauses:

1. Kada dete spava

   • dete is the subject of spava

2. televizor radi tiho

   • televizor is the subject of radi

Since both nouns are subjects in their own clauses, both are in the nominative.

It is not grammatically wrong, but it means something a little different.

• televizor radi tiho = the TV is on and playing quietly
• televizor je tih = the TV is quiet / silent

So radi tiho is better if you want to say the TV is operating at low volume.
Je tih focuses more on the TV’s state or quality, not on the action.

It can be understood either way depending on context.

• In a specific situation: When the child is sleeping, the TV is on quietly
• As a general habit: Whenever the child sleeps, the TV is on quietly

Serbian kada + present tense often allows both readings. Context decides whether it is a one-time situation or a repeated one.