Kanak-kanak itu cepat membesar.

This is called reduplication, and it is very common in Malay.

• kanak by itself is not normally used in everyday speech to mean child
• kanak-kanak is the standard word for children or young children

In Malay, reduplication often shows:

• plurality
• variety
• or a collective meaning

So kanak-kanak here refers to children as a group.

Usually, yes: kanak-kanak normally refers to children in general or to a group of children.

However, Malay does not always mark number as strictly as English does. Context often tells you whether something is singular or plural. Still, in normal usage, kanak-kanak is understood as plural or collective much more naturally than singular.

If you specifically want a child, learners will often see forms like:

• seorang kanak-kanak = a child
• budak = child/kid in more casual usage
• anak can also mean child, depending on context

In Malay, demonstratives such as ini and itu usually come after the noun.

So:

• kanak-kanak itu = those children / the children
• buku ini = this book
• rumah itu = that house

This is normal Malay word order. English puts words like this/that before the noun, but Malay usually puts ini/itu after it.

Itu literally often means that or those, but in many sentences it can also work a lot like the in English, especially when referring to something already known in the conversation.

So kanak-kanak itu could be understood as:

• those children
• the children

The best English translation depends on context.

Here cepat means quickly or fast, so it functions like an adverb in English.

One useful thing about Malay is that many words can work as either:

• an adjective
• or an adverb

without changing form.

For example:

• kereta cepat = a fast car
• berlari cepat = run quickly

So in cepat membesar, cepat means grow quickly.

Membesar means to grow, to grow bigger, or to grow up, depending on context.

It comes from:

• besar = big
• membesar = become big / grow

In this sentence, it means that the children grow quickly.

The mem- in membesar is part of the meN- verbal prefix system in Malay. This prefix often forms verbs.

Here:

• besar = big
• membesar = to become big / to grow

So the prefix helps turn the base idea into a verb.

You do not always need to analyze every prefix when reading, but it is useful to recognize that meN- often signals a verb in standard Malay.

Malay often does not use a verb like English to be in the same way.

English says:

• The children are growing quickly
• The children are big
• The children are happy

Malay often just places the relevant word or phrase after the subject:

• Kanak-kanak itu cepat membesar
• Kanak-kanak itu besar
• Kanak-kanak itu gembira

So the absence of is/are is completely normal in Malay.

The structure is:

• Kanak-kanak itu = subject
• cepat membesar = predicate

More specifically:

• kanak-kanak itu = the/those children
• cepat = quickly
• membesar = grow

So the order is basically:

Subject + adverb + verb

That is natural in Malay.

Usually, cepat membesar is the more natural order here.

You may also see:

• membesar dengan cepat = grow quickly

This version is also correct and can sound a little more explicit because dengan cepat clearly functions as an adverbial phrase.

So both are possible:

• Kanak-kanak itu cepat membesar
• Kanak-kanak itu membesar dengan cepat

The first is compact and very natural.

Malay verbs do not change form for tense the way English verbs do. So membesar itself does not specifically mean present, past, or future.

The time is understood from:

• context
• time words
• or the wider conversation

Without any time marker, Kanak-kanak itu cepat membesar is usually understood as a general present statement, something like:

• Those children grow quickly
• The children are growing quickly

If you want to make time clearer, Malay can add words such as:

• sedang = ongoing action
• sudah / telah = already, past/completed
• akan = future

Yes, that is also possible.

• anak-anak = children
• kanak-kanak = children / young children

The difference is mostly one of nuance:

• kanak-kanak often specifically refers to young children
• anak-anak is a broader word for children, depending on context

So both can work, but kanak-kanak emphasizes that they are children in the younger sense.