kodomo ga haita.

It is read:

こども が はいた。

A few notes:

• 子供 = こども
• が = ga
• 吐いた = はいた

So the whole sentence is kodomo ga haita.

One thing learners often notice: 吐いた is pronounced はいた, which sounds the same as 履いた (wore/put on, for shoes, pants, etc.). The kanji tells you which meaning it is.

が marks the subject of the sentence.

So in 子供が吐いた, 子供 is the thing/person that performed or experienced the action:

• 子供が = the child / the children as the subject
• 吐いた = vomited

A natural way to think about it is:

• It was the child who vomited
• The child vomited

In many basic sentences, が simply tells you who or what did the action.

This is a very common question.

Both が and は can appear after nouns, but they do different jobs:

• が marks the subject
• は marks the topic

So:

• 子供が吐いた focuses on who vomited
• 子供は吐いた means something more like as for the child, (they) vomited

Using が often sounds more like a direct report of an event or an answer to who did it?

For example:

• 誰が吐いたの？ = Who vomited?
• 子供が吐いた。 = The child did.

Using は could sound more contrastive, like:

• 大人は大丈夫だったけど、子供は吐いた。
• The adults were fine, but the child vomited.

So in a simple event-reporting sentence, が is very natural.

吐いた is the plain past form of the verb 吐く.

• Dictionary form: 吐く = to vomit, to spit out
• Plain past: 吐いた = vomited

This is how -く verbs like this typically change:

• 書く → 書いた
• 聞く → 聞いた
• 吐く → 吐いた

So 吐いた means the action happened in the past.

In this sentence, it is being used intransitively.

That means there is no direct object here; the sentence is just saying that the child vomited.

• 子供が吐いた。 = The child vomited.

However, 吐く can also be used in other ways, including with things that are emitted or spat out, depending on context. For example, it can be used for things like:

• smoke
• blood
• words
• breath

But in 子供が吐いた, the natural interpretation is simply vomited.

Because none is needed.

In English, vomit can work without an object too:

• The child vomited.

Japanese works the same way here:

• 子供が吐いた。

The sentence is complete as it is. Japanese often leaves out anything that is not necessary for understanding.

Yes. 吐いた is the plain form, so the sentence is casual/plain in style.

That does not automatically mean rude. Plain form is used all the time in:

• casual speech
• storytelling
• diary-style writing
• explanations
• internal thoughts

A polite version would be:

子供が吐きました。

So:

• 子供が吐いた。 = plain
• 子供が吐きました。 = polite

It can be singular or plural, depending on context.

Japanese nouns usually do not have to show singular/plural the way English does. So 子供 can mean:

• a child
• the child
• children
• the children

Context tells you which one is meant.

If you want to make the plural more explicit, you might say:

• 子供たち = children

But in many real sentences, Japanese leaves that unspecified.

Because Japanese does not use articles like English does.

English forces you to choose things like:

• a child
• the child

Japanese usually does not.

So 子供が吐いた does not itself tell you whether the English translation should be:

• A child vomited
• The child vomited

You decide that from context.

This is normal Japanese writing.

• 子供 is written with kanji
• が is a particle, so it is usually written in hiragana
• 吐いた has the verb stem in kanji (吐) and the ending in hiragana (いた)

This mix is extremely common in Japanese.

For verbs, the part written in hiragana after the kanji is called okurigana. It helps show the verb form, tense, and inflection.

The spaces are just for learning.

Normally, Japanese is written without spaces:

子供が吐いた。

Beginner materials often add spaces to make it easier to see the parts:

• 子供
• が
• 吐いた

But in normal Japanese writing, you usually will not see those spaces.

Yes.

Both 子供 and 子ども are common.

You may see:

• 子供
• 子ども

Many textbooks and educational materials prefer 子ども, while 子供 is also very widely used in everyday writing.

So if you already know the word as こども, both spellings are worth recognizing.

Yes.

That is a translation choice in English, not a change in the Japanese grammar.

吐いた can be translated naturally as:

• vomited
• threw up
• was sick (depending on context)

If the meaning has already been given to you, the main grammar point is simply that this is a past-tense sentence saying that the child did that action.