Learn Hardcore Japanese: genkina kodomotati ha kouen de sakkaa wo simasu. - The energetic children play soccer in the park.

You’ll still often see plain 子供 used even when English would say “children.”
Using 子供たち makes the “plural group of children” idea more explicit, and it often has a slightly “group of individuals” feeling.

What is the role of は in 子供たちは? Is it the subject marker?

は here is the topic marker, not strictly a “subject marker,” though the topic is often also the subject.

子供たちは… = As for the children, … / The children (on the other hand) …

It marks what the rest of the sentence is about. In this sentence, we’re talking about the energetic children, and then we say what they do: (they) play soccer in the park.

You could use が in some contexts:

元気な子供たちが公園でサッカーをします。

That sounds more like you’re presenting them as the grammatical subject, often with a feeling like “It is the energetic children who play soccer in the park” (focus on who does it).

With は, the tone is more like a neutral statement about the topic 元気な子供たち.

What does で mean in 公園で? How is it different from に?

In 公園でサッカーをします, the particle で marks the location of an action:

公園で = at/in the park (where the activity takes place)

Contrast with に:

公園に行きます。 = I will go to the park. (destination)
公園で遊びます。 = I will play at the park. (place of action)

Rough rule:

に → destination, existence, time
で → location where an action happens, means by which something is done, etc.

So 公園でサッカーをします = They do/play soccer in the park.

Why is there an を after サッカー? Isn’t サッカー just “soccer”?

Yes, サッカー is the noun soccer, and を is the direct object marker.

In Japanese, many activities are expressed as:

[noun] + を + する

Examples:

勉強をする = to study (do study)
練習をする = to practice (do practice)
ゲームをする = to play games
サッカーをする = to play soccer

So in:

サッカーをします
サッカー is treated as the thing being done, and を marks it as the object of the verb します (do).

Can I drop the を and just say サッカーします?

In everyday spoken Japanese, yes, many people say:

サッカーする
サッカーします

without を, and it’s perfectly natural and understood.

However:

In textbooks and more careful / formal speech, you’ll usually see サッカーをします.
Dropping を is common in speech, especially when it’s very clear what the object is.

So:

サッカーをします。 → textbook‑like, correct, slightly more careful
サッカーします。 → casual/spoken, also very natural

What exactly does します mean here? Why not する?

する is the plain (dictionary) form of the verb “to do.”
します is the polite form of the same verb.

In this sentence:

サッカーをする = to play soccer (plain)
サッカーをします = to play soccer (polite)

The sentence is in polite style overall, so we use します:

元気な子供たちは公園でサッカーをします。
→ Polite: “The energetic children play soccer in the park.”

If you were speaking casually to a friend, you might say:

元気な子供たちは公園でサッカーをする。

Does します here mean “do play,” “will play,” or “are playing”? The English tense seems different.

Japanese non‑past form (like します / する) covers present, habitual, and future meanings, depending on context.

サッカーをします can mean:

They play soccer (habitually).
They will play soccer.

English often translates it according to the context:

Talking about a routine:
→ “They play soccer in the park.”
Talking about a plan:
→ “They will play soccer in the park.”

If you want to emphasize something is happening right now, Japanese often uses 〜ている:

サッカーをしています。 = They are playing soccer (right now).

But even then, context is king, and the simple します often gets translated as “are playing” in basic examples.

Why is the word order [元気な] 子供たちは公園でサッカーをします? Can I change the order?

Japanese basic word order is often described as SOV (Subject–Object–Verb):

[Topic/Subject] + [location/time/etc.] + [object] + [verb]

In this sentence:

Topic/subject: 元気な子供たちは
Location: 公園で
Object: サッカーを
Verb: します

So: Children (topic) + at the park + soccer (object) + do.

You can move some parts around (as long as particles stay attached), for example:

元気な子供たちはサッカーを公園でします。
公園で元気な子供たちはサッカーをします。

These are still grammatical, but the default, neutral order is the one you saw. Changing the order can add subtle emphasis or sound slightly less natural if overdone. A safe rule for learners: keep the verb at the end and don’t separate nouns from their particles.

Why are there spaces between the words? Do Japanese people normally write like this?

In normal Japanese writing, there are no spaces between words:

元気な子供たちは公園でサッカーをします。

The version with spaces:

元気な　子供たち　は　公園　で　サッカー　を　します。

is made for learners, to help you see where the words and particles are.

Native texts:

No spaces
Rely on kanji, kana, and context for word boundaries

So: the spaces are just a teaching aid, not real-world Japanese writing style.

Why is 元気な before 子供たち? How do adjectives work with nouns in Japanese?

In Japanese, adjectives and other modifiers come before the noun they modify.

元気な子供たち
literally “energetic children”

Types:

い‑adjectives: e.g., 大きい犬 (big dog)
な‑adjectives: e.g., 静かな部屋 (quiet room), 元気な子供 (energetic child)

So:

元気な子供たち = “children who are energetic” / “energetic children”
You can’t put the adjective after the noun like English (“children energetic” is wrong in Japanese order).

If you want a full “relative clause” like “children who play soccer,” you still put it before the noun:

サッカーをする子供たち = children who play soccer

Could I say 元気な子供たちは公園でサッカーをしています instead? What is the difference from します?

Yes, you can say:

元気な子供たちは公園でサッカーをしています。

This uses 〜ている (しています) which often expresses:

An ongoing action:
→ The energetic children are playing soccer in the park (right now).
A current state resulting from an action, depending on the verb

Difference:

サッカーをします
→ general statement, habit, or future plan (play/will play soccer)
サッカーをしています
→ emphasizes that they’re currently in the middle of playing soccer

Both are correct; which one you choose depends on the context you want to express.