אם הילדים יבואו, ניקח עוד חטיפים ומיץ.

Because in Hebrew, a real future condition usually uses the future tense in both parts of the sentence:

• אם הילדים יבואו = if the children come / if the children will come
• ניקח עוד חטיפים ומיץ = we’ll take more snacks and juice

This is different from English, where we normally say If the children come, we’ll take... and not if the children will come.

So in Hebrew, future + future is normal here.

אם means if.

It introduces the condition:

• אם הילדים יבואו = if the children come

Then the second clause gives the result:

• ניקח עוד חטיפים ומיץ = we’ll take more snacks and juice

So the whole structure is:

• אם
  • condition
• result

This is a very common Hebrew pattern.

יבואו is the 3rd person plural future form of לבוא (to come).

Since הילדים means the children, the verb has to match a plural subject.

• singular masculine: הילד יבוא = the boy will come
• plural: הילדים יבואו = the children will come

Hebrew verbs usually agree with the subject in person, number, and sometimes gender.

In Hebrew, the masculine plural is the default form for:

• a mixed group of males and females
• a group whose gender is unspecified
• many general plural references

So הילדים יבואו is normal even if the group includes both boys and girls.

If you were specifically talking about girls, you would say:

• הילדות יבואו = the girls will come

Interestingly, in the future tense, יבואו is the same for masculine and feminine plural.

ניקח means we will take.

It is the 1st person plural future form of לקחת (to take).

So:

• אקח = I will take
• תיקח / תיקחי = you will take
• ייקח = he will take
• ניקח = we will take

The נ- at the beginning often marks we in the future tense.

Hebrew usually does not need a separate word for then in sentences like this.

So:

• אם הילדים יבואו, ניקח עוד חטיפים ומיץ.

already naturally means:

• If the children come, (then) we’ll take more snacks and juice.

The result clause follows directly, and that is enough.

Here עוד means more, additional, or extra.

So:

• עוד חטיפים ומיץ = more snacks and juice / additional snacks and juice

It often appears before the noun it modifies:

• עוד מים = more water
• עוד זמן = more time
• עוד ילדים = more children

In this sentence, it implies that some snacks and juice may already exist, and more will be taken if the children come.

Because את is used before a definite direct object, and here the object is indefinite.

Compare:

• ניקח חטיפים ומיץ = we’ll take snacks and juice
  no את, because the objects are not definite

• ניקח את החטיפים ואת המיץ = we’ll take the snacks and the juice
  here את appears because החטיפים and המיץ are definite

So in your sentence, no את is needed.

Because הילדים is definite: it means the children.

• ילדים = children
• הילדים = the children

But חטיפים and מיץ here are indefinite:

• חטיפים = snacks
• מיץ = juice

So the sentence is talking about the children specifically, but only some additional snacks and juice, not a specific known set.

Yes. Hebrew allows some flexibility.

For example, you can also say:

• ניקח עוד חטיפים ומיץ אם הילדים יבואו.

That means the same thing:
We’ll take more snacks and juice if the children come.

The version with the אם-clause first is very natural when the condition is being emphasized:

• אם הילדים יבואו, ניקח...

The version with the result first is also natural, especially in speech.

The comma is standard when the sentence begins with the if-clause:

• אם הילדים יבואו, ניקח עוד חטיפים ומיץ.

It helps separate the condition from the result.

If the order is reversed, a comma is often not needed:

• ניקח עוד חטיפים ומיץ אם הילדים יבואו.

So the punctuation here is normal and helpful.

A simple pronunciation guide is:

Im ha-yeladim yavo'u, nikakh od khatifim u-mitz.

A few notes:

• אם = im
• הילדים = ha-ye-la-dim
• יבואו = ya-vo-u
• ניקח = ni-kakh
  the final sound is the throaty kh sound, like Hebrew ח
• עוד = od
• חטיפים = kha-ti-fim
• ומיץ = u-mitz

The stress is roughly:

• ha-yelaDIM
• yaVO'u
• niKAKH
• kha-tiFIM

In this sentence, it sounds like a real future possibility:

• If the children come, we’ll take more snacks and juice.

Hebrew often uses this same structure for ordinary future conditions. It does not automatically sound unreal or impossible.

If the speaker wanted to express something more contrary-to-fact or impossible, Hebrew would usually use different wording and context.

So here, the sentence sounds practical and normal: the children may come, and if they do, the speaker will bring extra food and drink.