Стоит дочке взять пластилин, как она сразу начинает лепить.

This is a fixed Russian pattern meaning as soon as..., the moment..., or it only takes ... for ... to happen.

So:

Стоит дочке взять пластилин, как она сразу начинает лепить.

means something like:

As soon as my/the daughter takes some plasticine, she immediately starts modeling.

It often expresses a very quick, almost automatic reaction: one thing happens, and the other follows right away.

A very close English equivalent is:

No sooner does she get the plasticine than she starts modeling.

Because this construction often uses:

стоит + someone in the dative + infinitive

So дочке взять literally means something like:

for the daughter to take

The person who performs the infinitive is marked with the dative in this pattern.

Compare:

• Мне стоит только начать... = I only need to start...
• Ему стоит позвонить... = As soon as he calls...
• Дочке стоит взять пластилин... = As soon as the daughter takes the plasticine...

So дочке is not the direct object here; it is the person involved in the action взять.

No. Although стоить often means to cost, in this construction it does not mean that.

Here стоит is part of the idiomatic pattern стоит кому-то сделать..., как..., which means:

it only takes someone to do X for Y to happen

So you should not interpret it as The daughter costs to take plasticine... That would be wrong.

This use is related to the idea of it is enough / it only takes.

Because взять focuses on a single completed action: to take / pick up / get hold of.

In this sentence, that action is the trigger for what follows. The meaning is:

The moment she takes it, she starts modeling.

Perfective works well here because it marks the action as a specific event that sets off the next one.

If you used брать, it would sound less natural in this exact structure, because брать is imperfective and describes the process or repeated action more generally.

So:

• взять = a single taking event
• брать = taking in progress / repeated taking / general action

Пластилин is masculine and inanimate, so in the singular its accusative form is the same as the nominative form.

That is why:

• nominative: пластилин
• accusative: пластилин

Since взять takes a direct object, пластилин is in the accusative here, but it just happens to look the same as the dictionary form.

Compare with an animate masculine noun, where the accusative would change:

• взять брата = to take one’s brother
• but взять пластилин = to take plasticine

In this sentence, как is the second part of the fixed pairing стоит ..., как ....

So the structure is:

• first part: the trigger
• second part: what immediately happens after it

It does not mean how here.

You can think of it as part of a correlative construction:

Стоит дочке взять пластилин, как она сразу начинает лепить.

= As soon as the daughter takes plasticine, she immediately starts modeling.

The comma is required because this is a complex sentence with two linked clauses.

Начинает лепить emphasizes the start of the activity.

So the meaning is not just she models, but specifically:

she starts modeling right away

That fits well with the first clause, which describes the trigger. The whole sentence shows a sequence:

1. she takes the plasticine
2. she immediately starts modeling

If you said она сразу лепит, that would be understandable, but начинает лепить highlights the beginning of the action more clearly.

Because лепить describes the activity or process of modeling, not the completion of one finished object.

• лепить = to model / sculpt / shape something, as an ongoing activity
• слепить = to make something completely, to finish molding it

In this sentence, the point is that she begins the activity of playing with the plasticine and shaping it. It is about the process, so лепить is the natural choice.

If you said начинает слепить, that would be wrong, because after начинать Russian normally uses the infinitive of the activity, and imperfective is usually expected:

• начинает читать
• начинает писать
• начинает лепить

Yes, they refer to the same person, but they have different grammatical roles in different clauses.

In the first clause:

дочке is in the dative because of the pattern стоит кому-то взять...

In the second clause:

она is the normal nominative subject of начинает

So the sentence needs different forms because the grammar of the two clauses is different.

This is very natural in Russian:

• first clause: dative participant
• second clause: nominative subject

Usually it describes a habitual or typical situation.

The present-tense verbs стоит and начинает suggest something like:

Whenever she gets hold of plasticine, she immediately starts modeling.

So this is not necessarily about one specific moment. It is more like a general observation about her behavior.

If you wanted a one-time future meaning, Russian would usually phrase it differently.

It is natural Russian, but the pattern стоит ..., как ... is a little more expressive and slightly more literary than the plain everyday как только.

A more neutral alternative would be:

Как только дочка берёт пластилин, она сразу начинает лепить.

That means almost the same thing.

The original version sounds a bit more vivid, as if the second action follows instantly and almost inevitably.

Yes, Russian word order is flexible, though not completely free.

The given order is natural:

Стоит дочке взять пластилин, как она сразу начинает лепить.

You could also say:

Дочке стоит взять пластилин, как она сразу начинает лепить.

but the original sounds smoother and more standard.

Word order in Russian often affects emphasis rather than basic meaning. Here the sentence begins with the trigger construction right away, which makes the cause-and-immediate-result relationship very clear.