háizi tīngwán gùshi yǐhòu jiù shuìzháo le.

The sentence can be understood as:

孩子 + 听完故事以后 + 就 + 睡着了

A natural breakdown is:

• 孩子 = the child
• 听完故事以后 = after finishing listening to the story
• 就 = then / right away
• 睡着了 = fell asleep

So the structure is:

subject + after doing X + then + did Y

This is a very common Mandarin pattern for describing one event happening after another.

完 is a result complement. It shows that the action reaches completion.

So:

• 听故事 = listen to a story
• 听完故事 = finish listening to the story

In this sentence, 听完 tells you the child did not just listen for a while; the listening was completed.

This pattern is very common:

• 看完 = finish reading/watching
• 吃完 = finish eating
• 写完 = finish writing

So 听完故事以后 means after finishing the story or after listening to the whole story.

Yes, you could, but the meaning changes slightly.

• 听了故事以后 = after listening to the story
• 听完故事以后 = after finishing listening to the story

The version with 完 is more specific because it emphasizes completion. Without 完, the sentence is still grammatical, but it does not stress as clearly that the story was fully heard.

So in this sentence, 听完 fits well because it naturally leads into the next event: the child fell asleep after the story was finished.

以后 means after or afterward.

Here it comes after the phrase 听完故事, so together:

听完故事以后 = after finishing listening to the story

A useful rule is:

• verb phrase + 以后 = after doing something
• noun + 以后 = after something

Examples:

• 吃饭以后 = after eating
• 下课以后 = after class
• 回家以后 = after going home

So 以后 marks the earlier event and sets up what happens next.

就 often shows that something happens then, right away, or sooner than expected.

In this sentence:

• 听完故事以后就睡着了

This suggests a close connection between the two actions: the child finished hearing the story, and then promptly fell asleep.

Without 就, the sentence would still be possible, but 就 makes the sequence feel tighter and more immediate.

Compare:

• 听完故事以后，孩子睡着了。 = After listening to the story, the child fell asleep.
• 听完故事以后，孩子就睡着了。 = After listening to the story, the child then fell asleep / fell asleep right away.

This is a very common learner question.

• 睡觉 = to sleep / go to sleep / be sleeping in a general sense
• 睡着 = to fall asleep, or to become asleep

In this sentence, 睡着 is used because it focuses on the change of state: the child was awake, and then the child fell asleep.

So:

• 孩子睡觉了 can mean the child went to sleep / is sleeping
• 孩子睡着了 means the child actually fell asleep

That is why 睡着了 is especially natural here.

Because in 睡着, the character 着 is not the aspect marker zhe. Here it is pronounced zháo and acts as a result element.

In this pattern, V + 着 / 到 / 见 often shows that a result has been achieved.

So:

• 睡着 = succeed in falling asleep
• 看着 in this sense is not the same kind of pattern
• 找到 = find successfully
• 听见 = hear successfully

For learners, it helps to memorize 睡着 as a fixed expression meaning to fall asleep.

The final 了 shows that a new situation has occurred or that the event has been realized.

In 睡着了, it marks the fact that the child has now fallen asleep.

This is very natural because falling asleep is a change of state:

• before: awake
• after: asleep

So 了 here does not just mean past tense. It marks that the state changed.

That is why 睡着了 sounds more complete and natural than just 睡着 in this sentence.

Because 孩子 here is being used as the subject in a simple, general way: the child or the kid.

In Mandarin, nouns do not always need a measure word. Measure words are required in patterns like:

• 一个孩子 = one child
• 那个孩子 = that child
• 这孩子 = this child

But when a noun stands alone as the subject, it can often appear without one:

• 孩子睡着了。 = The child fell asleep.
• 老师来了。 = The teacher came.
• 妈妈回家了。 = Mom came home.

So 孩子 by itself is perfectly normal here.

Because 听 is the verb and 故事 is its object.

The core verb-object relationship is:

• 听故事 = listen to a story

When 完 is added as a result complement, it goes after the verb:

• 听完故事

So the order is:

verb + result complement + object

not:

• 听故事完 ✘

This is the normal word order for this kind of complement in Mandarin.

Yes, often it can.

• 听完故事以后
• 听完故事后

Both mean after finishing the story.

The version with 以后 is a little fuller and very common in everyday speech.
The version with 后 is slightly shorter and can sound a bit more compact or written, though it is also common in speech.

So in this sentence, either works, but 以后 is very natural for learners to know and use.

Most likely it refers to a specific child in context, even though English may need the child.

Mandarin often leaves that kind of definiteness unmarked. So 孩子 can mean:

• the child
• a child
• children, in some contexts

Here, because the sentence describes a single event sequence, the most natural interpretation is the child.

This is one reason Mandarin often feels less explicit than English about a/the distinctions.