kodomo ha siai de kouhunsita.

A natural reading is:

こども は しあい で こうふんした。
Kodomo wa shiai de kōfun shita.

A few notes:

• 子供 = こども
• 試合 = しあい
• 興奮した = こうふんした
• The は particle is written ha but pronounced wa here.

When は is used as the topic particle, it is pronounced wa, not ha.

So in this sentence:

• 子供は = As for the child / the children...

This is a very common beginner point:

• は as a normal syllable in a word: pronounced ha
• は as a particle: pronounced wa

は marks the topic of the sentence.

So 子供は means something like:

• As for the child...
• The child...
• The children...

In many simple sentences, は can feel similar to an English subject marker, but it is not exactly the same as English is/does structure. It tells the listener what the sentence is about.

Here, the sentence is talking about the child / the children, and then says what happened regarding them.

It can mean either, depending on context.

Japanese nouns usually do not automatically show singular vs. plural the way English does. So 子供 can mean:

• child
• children

If the broader context does not make it clear, the English translation has to choose one. Japanese itself often leaves that unspecified.

If you really want to make it clearly plural, Japanese can use forms like:

• 子供たち = children

But in many natural sentences, plain 子供 is enough.

Japanese does not normally use articles like English a, an, and the.

So 子供 can mean:

• a child
• the child
• children
• the children

And 試合 can mean:

• a game
• the game
• a match
• the match

The exact meaning is understood from context.

In this sentence, で marks the setting or situation in which something happened.

So 試合で means something like:

• at the game
• during the game
• in the match

Here it does not mean with in the tool/instrument sense, and it does not mean the game directly caused excitement in a strict grammatical way. It simply gives the context where the excitement happened.

So the structure is roughly:

• 子供は = as for the child
• 試合で = at/during the game
• 興奮した = became excited / got excited

This is a very natural question, because both で and に can sometimes be translated as at.

Here, で is used because the game is treated as the event/situation in which the excitement happened.

• 試合で興奮した = got excited at/during the game

If you used に, it would sound different and would usually need a different structure or meaning. に often marks:

• a destination
• a specific point in time
• a target of emotion or action
• existence location with いる / ある

So 試合で is the natural choice for during the game / in the context of the game.

No. 興奮した is the past tense of the verb 興奮する.

• dictionary form: 興奮する = to get excited / to be excited
• past form: 興奮した = got excited / was excited

This is a suru-verb, which is a very common Japanese pattern:

• 勉強する = to study
• 心配する = to worry
• 興奮する = to get excited

So even though excited is often an adjective in English, in Japanese this expression is commonly verbal.

It can suggest either one, depending on context.

Literally, 興奮した is the past form of 興奮する, so it often has the sense of:

• became excited
• got excited
• was excited

In many real translations, English chooses whichever sounds most natural.

If you want to emphasize an ongoing state more clearly, Japanese might use something like:

• 興奮していた = was excited / was in an excited state

So 興奮した can sometimes feel a little more like the excitement arose, while 興奮していた can emphasize that the state continued.

Because Japanese is basically an SOV language: Subject/Topic – Object/Other information – Verb.

English often puts the verb earlier:

• The child got excited at the game.

Japanese usually puts the main verb at the end:

• 子供は 試合で 興奮した。

This is one of the most important word-order differences between English and Japanese.

Yes. In normal Japanese writing, you would usually write it as:

子供は試合で興奮した。

The spaces in your example are just there to help learners see the parts more easily.

Usually, 試合で most naturally means at the game or during the game, not for the game in the sense of anticipation.

If you want to say someone was excited about a game or for an upcoming game, Japanese would often use a different expression, such as:

• 試合に興奮した in some contexts, though this can sound less neutral depending on nuance
• 試合を楽しみにしていた = was looking forward to the game
• 試合のことで興奮していた = was excited about the game

So in your sentence, the most straightforward reading is that the excitement happened in the context of the game itself.

Yes, it is understandable and natural.

That said, depending on the exact nuance, native speakers might also choose slightly different phrasing, for example:

• 子供は試合で興奮していた。
  This emphasizes that the child was in an excited state during the game.

• 子供は試合を見て興奮した。
  This makes it clearer that the child got excited watching the game.

But 子供は試合で興奮した。 is a perfectly valid sentence.