Learn Hardcore Japanese: kodomo no hyouzyou wo mite, haha ha ansinsimasita. - The mother felt relieved when she saw the child's expression.

Literally, it’s “seeing (looking at) the child’s expression”.
If you said 子供を見て, that would mean “seeing the child” in a more general sense, not focusing specifically on the facial expression.

What does the particle の do in 子供の表情?

Here の shows a possessive or attributive relationship:

A の B ≈ B of A or A’s B

So:

子供の表情 = the expression of the child, the child’s expression

This is the same の you see in:

私の本 – my book
日本の文化 – Japanese culture

In this sentence 子供 is not the direct object; it’s just describing which expression (the child’s one).

What is the function of 見て here? Why isn’t it just 見ます or 見た?

見て is the て-form of 見る. The て-form is often used to connect two actions or clauses.

Pattern here:
[Action/State] て、[Result / Next action]

In this sentence:

子供の表情を見て、 – seeing / after seeing / on seeing the child’s expression,
母は安心しました。 – the mother felt relieved.

So 見て can imply:

“after seeing”
or “on seeing” / “when she saw”
or “seeing … , (she then) …”

Using 見ます or 見た would break that smooth connection and would create a separate sentence, not a single flowing cause–result or sequence.

Does 子供の表情を見て、母は安心しました mean that seeing the expression is the reason she felt relieved, or just something that happened first?

It can express both sequence and cause, and in natural reading it’s usually understood as both:

She saw the child’s expression → that’s why she felt relieved.

The て-form often carries a slight causal nuance in contexts like this. You could paraphrase as:

“Because she saw the child’s expression, the mother felt relieved.”
“Upon seeing the child’s expression, the mother felt relieved.”

So it’s not just “first this, then that”; it sounds like the expression reassured her.

Why is it 母は and not お母さんは? Are they different in nuance?

Yes, there’s a nuance difference:

母 – neutral/“my mother” in narration, somewhat formal/literary; used when talking about one’s own mother to outsiders or in written style.
お母さん – polite / familiar word used:
- when addressing your mother, or
- when referring politely to someone else’s mother.

In third-person narration (like in a story), 母 often refers to “the mother (of the child being talked about)”.
If you said お母さんは安心しました, it would sound more like dialogue or casual family talk (e.g., a child talking about their own mom), or like you’re being polite toward someone else’s mother.

What exactly does 安心しました mean? Is it “was relieved,” “felt relieved,” or “became relieved”?

安心しました comes from:

安心する – to feel relieved, to be at ease, to be reassured.
しました – polite past form of する.

It often implies a change of state:

She became relieved / came to feel relieved at that moment.

In natural English, you’d usually say:

“(The mother) felt relieved.”
or “(The mother) was relieved.”

So you can think:
安心しました = “(she) became in a state of安心 (relief).”

Why is the verb in the past tense (安心しました) if in English we might say “the mother feels relieved”?

Japanese often uses the past tense to describe a completed change of state:

At the moment she saw the child’s expression, her emotional state changed to “relieved”.

So 安心しました marks that shift as a completed event in the story timeline.

In English, we might say either:

“The mother was relieved.” (simple past)
“The mother feels relieved.” (present, describing her current state)

Japanese will still typically use しました in this narrative context, even if English could use present tense.

What does 表情 literally mean, and how is it different from just saying 顔?

表情（ひょうじょう） literally: “expression on the surface (of the face)”.
- 表 – surface, outside
- 情 – feelings, emotion

So 表情 refers specifically to facial expression that shows emotion.

Difference:

顔（かお） – the face itself (the physical thing).
表情 – the expression on that face (smile, worry, fear, etc.).

You could say 子供の顔を見て (“seeing the child’s face”), but 子供の表情を見て focuses on what the expression communicated, which fits better with the idea of the mother being reassured by what she saw.

Could I say 子供の顔を見て、母は安心しました instead? Would that be wrong?

It wouldn’t be wrong; it’s grammatically fine and understandable:

子供の顔を見て、母は安心しました。
→ “Seeing the child’s face, the mother felt relieved.”

However, the nuance shifts slightly:

顔 – more neutral: she saw the face.
表情 – emphasizes the expression that shows how the child is doing.

Since relief usually comes from reading someone’s expression (they look healthy, calm, happy, etc.), 表情 is more precise and natural here.

Is 母は the grammatical subject here? Why don’t we say “she” or “the mother” explicitly like in English?

In Japanese:

母は marks the topic with は.
Often, the topic also functions as the subject, especially with verbs like 安心しました (to feel relieved).

So effectively:

母は安心しました。 ≈ “The mother felt relieved.”

Japanese typically omits pronouns like “she”/“he” when the referent is clear from context.
Instead of saying “she,” Japanese:

introduces or recalls the topic with は (here: 母は), then
gives information about that topic (here: 安心しました).

So yes, 母 is the one who felt relieved, and は marks it as the topic (and de facto subject in this sentence).