Ребёнок кашлянул и начал плакать.

Ребёнок is the nominative singular form, because it is the subject of the sentence: the child is the one doing the actions.

A few useful details:

• Dictionary form: ребёнок
• Meaning: child
• Gender: masculine grammatically
• Plural: дети (children) — this is irregular and very common

Because ребёнок is the subject, it stays in the basic subject form.

In the past tense, Russian verbs agree with the subject in gender and number.

Since ребёнок is grammatically masculine singular, the verbs are also masculine singular:

• кашлянул = masculine past
• начал = masculine past

Compare:

• ребёнок кашлянул и начал плакать = the child coughed and began to cry
• девочка кашлянула и начала плакать = the girl coughed and began to cry

So the -л past-tense form changes depending on gender/number:

• masculine: -л
• feminine: -ла
• neuter: -ло
• plural: -ли

This is an aspect question.

• кашлянул is perfective
• кашлял is imperfective

Here, кашлянул usually means gave a cough / coughed once — a single, brief action.

By contrast, кашлял suggests:

• repeated coughing,
• coughing for some time,
• or simply describing the process without focusing on one completed act.

So:

• Ребёнок кашлянул = the child coughed once
• Ребёнок кашлял = the child was coughing / coughed repeatedly

In this sentence, кашлянул fits well because it sounds like a short event that happened before the crying started.

After начать (to begin/start), Russian normally uses the infinitive, not another finite verb form.

So:

• начал плакать = began to cry
• начал плакал = incorrect

This is similar to English began to cry rather than something like began cried.

A very common pattern is:

• начать + infinitive

Examples:

• начал говорить = began to speak
• начала смеяться = began to laugh
• начали работать = began to work

After начал, Russian usually uses an imperfective infinitive to describe the action that started.

So:

• начал плакать = began crying / began to cry

The focus is:

1. the starting point (начал),
2. plus the action as a process (плакать).

That is why плакать is natural here.

A learner may wonder about заплакать. That verb is perfective and means something like to start crying / burst into tears. So Russian can also say:

• Ребёнок кашлянул и заплакал.

That is perfectly natural too, but it is slightly different in structure:

• начал плакать = explicitly says began to cry
• заплакал = a single perfective verb meaning started crying

Both are common; the sentence you have uses the begin + infinitive pattern.

Because и is joining two verbs with the same subject inside one simple sentence:

• кашлянул
• начал плакать

Both actions belong to ребёнок.

So this is basically one subject with two coordinated predicates, and Russian does not put a comma before и in this kind of structure.

Compare:

• Ребёнок кашлянул и начал плакать. = no comma

But if you had two separate clauses with different structure, punctuation rules could change.

Russian does not need to repeat the subject if it is clearly the same.

So:

• Ребёнок кашлянул и начал плакать.

is completely natural, and repeating он would usually be unnecessary.

English also often does this:

• The child coughed and began to cry.

You do not say:

• The child coughed and he began to cry
  unless you want extra emphasis or contrast.

Russian works similarly here.

Yes. They are related verbs:

• кашлять = to cough, to be coughing, to cough repeatedly
• кашлянуть = to give a cough, to cough once

This is a common Russian pattern where a verb in -ну- can express a single short action.

So:

• кашлять = ongoing/repeated coughing
• кашлянуть = one quick cough

That is why кашлянул works so well in this sentence: it sounds like one brief cough before the next action.

Yes, in many real-life texts you will often see е written instead of ё, so ребенок is very common in print.

But the standard pronunciation is with ё:

• ребёнок

Important points:

• ё always indicates the sound yo
• ё is always stressed
• many Russian texts omit the dots and write е instead, even though the word is still pronounced with ё

So for learners, it is very helpful to remember the real form as ребёнок.

The stressed syllables are:

• ребЁнок
• кашлЯнул
• и
• начАл
• плакАть

So the sentence is pronounced roughly like:

reb-YO-nak kash-LYA-nool ee na-CHAL pla-KAT'

A few notes:

• ё in ребёнок automatically shows the stress
• начал is stressed on the second syllable: начАл
• плакать is stressed on the first а after л: плакАть

Stress is very important in Russian, so this is worth memorizing together with the words.

Yes. Russian word order is more flexible than English word order because grammatical endings carry a lot of information.

The neutral order here is:

• Ребёнок кашлянул и начал плакать.

But other orders are possible for emphasis, for example:

• Кашлянул ребёнок и начал плакать.
• Начал плакать ребёнок после того, как кашлянул.
  (this changes the structure more noticeably)

Still, the original version is the most straightforward and natural in ordinary narration.

For learners, the key point is:

• Russian word order can move around,
• but the default sentence you have is normal and neutral.

Not exactly, though they are often close in meaning.

• начал плакать = began to cry
• заплакал = started crying / burst into tears

The difference is mostly one of nuance and structure:

• начал плакать explicitly highlights the beginning of a process
• заплакал is a single perfective verb that packages the beginning into one action

In many contexts, both would translate similarly. But Russian often chooses between them based on style and nuance.

For example:

• Ребёнок кашлянул и начал плакать.
  Slightly more descriptive of the process beginning.

• Ребёнок кашлянул и заплакал.
  Slightly more compact and event-like.

Both are natural.