Les enfants ont peur de la punition, alors ils se taisent.

In French, nouns normally need an article. So les enfants means the children.

French does not usually drop the article the way English can in some general statements. You would not normally say just Enfants as the subject of a full sentence.

Also, les can mean either:

• the children in a specific situation, or
• children in a general sense, depending on context

So Les enfants ont peur... can sound natural even if English might simply say Children are afraid... in some contexts.

French often uses the expression avoir peur de, which literally means to have fear of, but it simply means to be afraid of.

So:

• avoir peur de quelque chose = to be afraid of something
• avoir peur de quelqu’un = to be afraid of someone

This is just the normal French structure. A direct equivalent of English to fear exists, craindre, but avoir peur de is much more common in everyday speech.

So Les enfants ont peur de la punition is the natural everyday way to say that the children are afraid of punishment.

After avoir peur, French normally uses de before the thing or person feared.

So the pattern is:

• avoir peur de + noun
• avoir peur de + infinitive

Examples:

• J’ai peur du chien. = I’m afraid of the dog.
• Elle a peur de tomber. = She is afraid of falling.

In your sentence, de links peur to la punition:

• ont peur de la punition = are afraid of punishment

French usually keeps an article before a noun here. So de la punition is normal.

This can mean:

• the punishment, if a specific punishment is understood from context, or
• punishment in a general sense

French often uses the definite article where English uses no article at all, especially with general ideas or abstract nouns.

Compare:

• avoir peur de la mort = to be afraid of death
• parler de la justice = to talk about justice

Also, de only contracts with le and les:

• de + le = du
• de + les = des

But with la, there is no contraction, so:

• de la punition is correct

Here, alors means so, therefore, or as a result.

It connects the two ideas:

• they are afraid of punishment
• as a result, they keep quiet

So it shows consequence.

Depending on context, alors can also mean then, but in this sentence so or therefore is the best sense.

Because French normally requires an explicit subject before a conjugated verb.

In English, you also repeat the subject in a sentence like:

• The children are afraid of punishment, so they keep quiet.

French works the same way here:

• Les enfants ... alors ils ...

You cannot normally omit ils in a standard sentence.

Se taisent comes from the infinitive se taire, which means:

• to be quiet
• to keep quiet
• to fall silent
• to shut up in stronger contexts

In this sentence, ils se taisent means they keep quiet or they fall silent.

This verb is somewhat irregular. In the present tense:

• je me tais
• tu te tais
• il / elle se tait
• nous nous taisons
• vous vous taisez
• ils / elles se taisent

So se taisent is the they form.

Not literally. Se taire is a pronominal verb, and it is simply the normal dictionary form.

In many French verbs with se, the reflexive idea is weaker or idiomatic. Here, se taire does not really mean to silence themselves word for word in normal usage. It just means to keep quiet or to become silent.

So when learning it, it is best to remember the whole expression:

• se taire = to keep quiet

And then conjugate it with the reflexive pronoun:

• je me tais
• ils se taisent, etc.

Because in French, many -er, -re, and irregular verbs in the ils/elles form end in -ent, but that ending is usually not pronounced.

So:

• ils parlent → the -ent is silent
• ils mangent → the -ent is silent
• ils se taisent → the -ent is silent

That means taisent is pronounced roughly like tèz, not with a spoken ent at the end.

A careful approximate pronunciation is:

Lay zahn-fahn zon purr duh lah pew-nee-see-ohn, ah-lor eel suh tez.

A few important points:

• Les enfants has a liaison: the s of les sounds like z before enfants
• enfants has a nasal vowel
• ont also links smoothly to the next word in connected speech
• se taisent ends with a silent -ent

A more natural rhythm would be something like:

Les enfants / ont peur de la punition, / alors ils se taisent.

Both verbs are in the present indicative:

• ont = from avoir
• se taisent = from se taire

The present tense can describe:

• something happening now
• a general truth
• a habitual reaction

Here it most naturally describes a general or immediate situation:

• the children are afraid of punishment
• so they keep quiet

French uses the present here just as English often does.

Sometimes, but keep quiet or fall silent is better here.

Se taire usually suggests an action or reaction: becoming quiet or choosing not to speak.

If you said ils sont silencieux, that would describe their state more statically:

• ils sont silencieux = they are silent
• ils se taisent = they keep quiet / they fall silent

In this sentence, because their silence is a result of fear, se taisent is the more natural choice.