الطفل خائف من المطر.

Because this is a nominal sentence in Arabic. In the present tense, Arabic usually does not use a separate word for is/am/are.

So:

• الطفل = the child
• خائف = afraid
• من المطر = of the rain / from the rain

Together: The child is afraid of the rain.

If you wanted a past-tense version, Arabic would use a verb such as كان:

• كان الطفل خائفًا من المطر = The child was afraid of the rain.

الطفل is the subject of the sentence.

In a nominal sentence like this, the first noun is often called the مبتدأ (the topic/subject), and what comes after it gives information about it.

So here:

• الطفل = the subject
• خائف = the predicate / description
• من المطر = a prepositional phrase completing the meaning of خائف

So the structure is basically:

[The child] [afraid] [of the rain].

خائف means afraid or fearful.

It comes from the verb خاف = to fear / to be afraid.

So you can think of خائف as an adjective-like word meaning:

• afraid
• fearful

Examples:

• أنا خائف = I am afraid
• هي خائفة = She is afraid

In this sentence, خائف is not a finite verb like fears or is afraid. It is an active participle used like an adjective or predicate.

That means it behaves a lot like an adjective in this sentence:

• الطفل خائف = The child is afraid

Compare with the verb form:

• الطفل يخاف من المطر = The child fears / is afraid of the rain

Both are natural, but they are built differently:

• خائف = a descriptive word
• يخاف = an actual verb

Because خائف commonly takes من to mean afraid of.

So:

• خائف من شيء = afraid of something

Examples:

• خائف من الكلب = afraid of the dog
• خائفة من الامتحان = afraid of the exam

Even though من often means from, after words like خائف it is best understood as part of the expression afraid of.

المطر means the rain, with the definite article الـ.

Arabic often uses the definite form in places where English may or may not use the, especially when speaking about something understood in context or about a general phenomenon.

So:

• مطر = rain
• المطر = the rain

In this sentence, من المطر is very natural and means of the rain / because of the rain.

In fully vocalized Arabic, the sentence would usually be:

الطِّفْلُ خائِفٌ مِنَ المَطَرِ

The endings are:

• الطفلُ: -u because it is the subject of the nominal sentence
• خائفٌ: -un because it is an indefinite predicate
• المطرِ: -i because it comes after the preposition من

In normal everyday writing, these short vowels are usually not written:

• الطفل خائف من المطر

A helpful pronunciation is:

khā'if

Points to notice:

• خ is a throaty sound, like the ch in Scottish loch or German Bach
• ائ includes a hamza stop in the middle
• So it is not one smooth syllable like khaif
• It is more like khaa-if

A rough guide:

• خا = khaa
• ئف = 'if

So: khā'if

Because in this kind of sentence, the predicate is usually indefinite.

So Arabic says:

• الطفل خائف not normally
• الطفل الخائف if you mean The child is afraid

The form الطفل الخائف means something different:
it means the afraid child or the fearful child, where الخائف directly modifies الطفل as an adjective inside a noun phrase.

So compare:

• الطفل خائف = The child is afraid
• الطفل الخائف = the afraid child

Yes. That is also correct and natural.

Difference:

• الطفل خائف من المطر = The child is afraid of the rain
  This describes the child’s state.

• الطفل يخاف من المطر = The child fears / is afraid of the rain
  This uses the verb يخاف and can sound a bit more verbal or dynamic.

In many contexts, both are fine.

Then خائف must agree in gender with the subject.

You would say:

الطفلة خائفة من المطر
= The girl is afraid of the rain

So:

• masculine: خائف
• feminine: خائفة

Agreement is important here.

Literally, من often means from, yes. But in this sentence, it is best translated by meaning, not word-for-word.

So:

• literal pieces: from the rain
• natural English meaning: afraid of the rain

This is very common in Arabic: a preposition may not match the English preposition exactly.

Yes, but الطفل خائف من المطر is the most straightforward order.

This order is:

1. subject
2. predicate
3. prepositional phrase

Arabic can sometimes change word order for emphasis, but for learners, this is the best basic pattern to remember.

So the standard version is:

الطفل خائف من المطر

You keep من المطر and change the subject and the form of خائف as needed.

Examples:

• أنا خائف من المطر = I am afraid of the rain
  (said by a male)

• أنا خائفة من المطر = I am afraid of the rain
  (said by a female)

• نحن خائفون من المطر = We are afraid of the rain
  (masculine or mixed group)

• هنَّ خائفات من المطر = They are afraid of the rain
  (all female)

So خائف changes for gender and number.