Learn Hardcore Japanese: kodomo mitai ni kouen de hasirimasita.

子供みたい by itself means “(someone is) like a child” or “seems like a child.”
When you want to use みたい to modify a verb or adjective, you usually add に:
- 子供みたいに走る = “to run like a child.”
みたいだ is just みたい + だ, used to end a sentence politely or more clearly:
- 彼は子供みたいだ。 = “He is like a child.”

So in your sentence, 子供みたいに means “in a childlike way / like a child” and it modifies the verb 走りました (“ran”).

Why do we use the particle に after みたい?

Here, に turns 子供みたい into something like an adverbial phrase—a phrase that describes how the action is done.

子供みたい = “(is) like a child” (describes a noun or is used at the end of a sentence)
子供みたいに = “in a childlike way / like a child” (describes a verb: how you ran)

So:
子供みたいに公園で走りました。
= “(I) ran in the park like a child.”

The pattern is:

Noun + みたいに + Verb
- 子供みたいに笑う = “laugh like a child”
- 大人みたいに話す = “speak like an adult”

Why is there no explicit “I” in the Japanese sentence?

Japanese often omits the subject when it is clear from context.
In conversation, if you are talking about what you did, it is understood that the subject is “I”, even if it is not said.

So:

子供みたいに公園で走りました。
Literally: “(Like a child) (at the park) ran.”
Naturally: “I ran in the park like a child.”

If you really want to spell it out, you could say:

私は子供みたいに公園で走りました。
But in normal speech, 私は is usually dropped if it’s obvious.

Why is 公園 followed by で and not に?

で marks the location where an action takes place.
に often marks a destination or location of existence.

公園で走る = “run in the park” (the park is where the running happens)
公園に行く = “go to the park” (the park is the destination)
公園にいる = “be at the park” (existence location)

In your sentence, 走りました is an action, so 公園で is correct:
公園で走りました。 = “(I) ran in the park.”

What tense and politeness level is 走りました, and what is its dictionary form?

Dictionary form: 走る = “to run”
走りました is:
- past tense (ran)
- polite form (the ます form in the past)

Form breakdown:

走る → 走ります (polite non-past: run / will run)
走ります → 走りました (polite past: ran)

So 走りました = “(I) ran” in a polite way.

Could I also say 子供のように公園で走りました? What is the difference between みたいに and ように?

Yes, you can say:

子供のように公園で走りました。

The meaning is essentially the same: “I ran in the park like a child.”

Nuance:

みたいに
- Very common in spoken, casual Japanese
- Slightly softer / more conversational in feel
ように
- More formal / neutral / written
- Often used in more careful or polite speech and writing

So:

Casual speech (talking with friends):
- 子供みたいに公園で走った。
More formal / neutral:
- 子供のように公園で走りました。

Your original sentence mixes casual-style expression (みたいに) with polite verb (走りました), which is very common in everyday conversation.

Is the mixture of casual-sounding みたいに with polite 走りました natural?

Yes, it is very natural.

Modern spoken Japanese often mixes casual grammar elements like みたいに, って, etc., with polite ます / です forms, especially in conversation with people you are not super close to but still speak fairly informally with.

More examples:

昨日は子供みたいに遊びました。 = “Yesterday I played like a child.”
ドラマみたいにうまくはいきませんでした。 = “It didn’t go as smoothly as in a drama.”

If you wanted to be uniformly more formal/written, you could use ように:

子供のように公園で走りました。

Can I change the word order, like 公園で子供みたいに走りました? Does it change the meaning?

Yes, you can change the word order:

子供みたいに公園で走りました。
公園で子供みたいに走りました。

Both are grammatically correct and basically mean the same thing:
“I ran in the park like a child.”

Nuance of word order in Japanese is usually about emphasis or flow, not grammar:

子供みたいに公園で走りました。
- Slightly emphasizes “like a child” first: “Like a child, I ran in the park.”
公園で子供みたいに走りました。
- Slightly emphasizes the place first: “At the park, I ran like a child.”

But in normal conversation, the difference is very small; both are natural.

Why is there no particle after 子供?

In the pattern:

Noun + みたいに + Verb

the noun (子供) directly modifies みたい, so you do not add another particle between them.

Correct:

子供みたいに走る。
Incorrect:
子供のみたいに走る。
子供はみたいに走る。 (ungrammatical in this pattern)

Similarly:

大人みたいに話す。 = “to speak like an adult”
プロみたいにプレーする。 = “to play like a pro”

So 子供みたいに is a fixed grammar pattern, not 子供 + particle + みたいに.

Does 子供みたいに mean “literally like a child” or “childishly”? What is the nuance?

子供みたいに can mean either, depending on context and tone:

Literally like a child (in a positive or neutral way)
- Running around full of energy, enjoying yourself, carefree.
- 昨日は子供みたいに公園で遊んだ。
  = “Yesterday I played in the park like a child.” (happy, nostalgic tone)
Childishly / immaturely (a slightly negative nuance)
- If said with a critical tone or about an adult’s behavior.
- いい大人なのに子供みたいに怒る。
  = “Even though he’s a grown adult, he gets angry like a child.”

In your sentence 子供みたいに公園で走りました。, with no negative context, it’s most naturally understood as happy, energetic, carefree—more like “I ran around in the park like a little kid (full of joy).”

What is the difference between 子供, 子ども, and 子供たち?

子供 (kanji)
- Standard modern writing. Very common in print.
子ども (kana + kanji)
- Also common, especially in texts about education or where people want to avoid any negative nuance in the kanji 供. Some style guides prefer this.
Meaning of both 子供 and 子ども is simply “child / children.” Number is often determined by context.
子供たち / 子どもたち
- たち is a plural-like ending, so this specifically emphasizes “children” (plural).
- 子供たちが公園で走りました。 = “The children ran in the park.”

In 子供みたいに, 子供 is being used in a generic sense: “like a (typical) child.”

Why are there spaces between the words if Japanese usually does not use spaces?

Standard Japanese writing does not use spaces between words.
The sentence would normally be written as:

子供みたいに公園で走りました。

The spaces in 子供　みたい　に　公園　で　走りました。 are there for learners, to help you see the word boundaries and particles:

子供 – “child”
みたい – “like / as if”
に – particle making it adverbial
公園 – “park”
で – location-of-action particle
走りました – “ran” (polite past)

So in real Japanese texts, write it without the spaces.