Стоит мне открыть банку варенья, как дети сразу просят горячий хлеб из тостера.

Here стоит is part of the fixed construction стоит + dative + infinitive, как..., which means it only takes someone to do something, and then... or more naturally as soon as....

So:

Стоит мне открыть банку варенья, как...
= As soon as I open a jar of jam...
= The moment I open a jar of jam...

This is not the literal stands meaning, and not really the usual costs meaning either, even though it is the same verb form.

Because this construction uses the dative case for the person involved:

стоит кому + infinitive

So:

• мне = to me
• тебе = to you
• ему = to him

In other words, Russian says something like:

It only takes for me to open...

That is why мне appears instead of nominative я.

This is a very common Russian pattern meaning as soon as X happens, Y happens.

Structure:

Стоит + person in dative + infinitive, как + main clause

Example from your sentence:

Стоит мне открыть банку варенья, как дети сразу просят...

Literally, it is close to:

It only takes me to open the jar of jam, and the children immediately ask...

But in natural English:

As soon as I open the jam jar, the children immediately ask...

This construction often suggests a repeated or typical reaction, sometimes with a slight feeling of every single time this happens.

Because after стоит кому you use an infinitive.

So the pattern is not:

• стоит мне открываю ❌
• стоит мне открою ❌

but:

• стоит мне открыть ✔

Here открыть is the perfective infinitive, because the sentence refers to a single completed action: to open the jar.

Because открыть is perfective, and this construction usually points to a specific action being completed.

• открыть = to open, successfully/open completely
• открывать = to be opening / to open repeatedly / process-oriented

In this sentence, the idea is:

The moment I open the jar...

That is a completed trigger event, so открыть is the natural choice.

This is a standard Russian noun pattern:

банка чего? = a jar of what?

So:

• банка = jar
• банка варенья = jar of jam/preserves

When one noun specifies the contents or type of another noun, Russian often uses the genitive case:

• чашка чая = a cup of tea
• бутылка воды = a bottle of water
• банка варенья = a jar of jam

In your sentence, банку is accusative singular because it is the direct object of открыть, while варенья stays genitive because it depends on банка.

Варенье is a sweet fruit preserve. Translating it as jam is usually fine, though it is not always exactly the same as English-style jam.

Very roughly:

• варенье often has visible pieces of fruit or whole berries in syrup
• English jam can be smoother or more mashed

But for normal learning purposes, jam or preserves is a good translation.

Yes, как often means how, but in this construction it has a different function.

In Стоит мне..., как..., the word как introduces the result that follows immediately after the trigger action.

So here it works as part of the whole pattern meaning:

as soon as... then...

You should learn стоит мне..., как... as one chunk, rather than trying to interpret как by itself.

Because the sentence describes a habitual, repeated situation:

Whenever I open a jar of jam, the children immediately ask...

Russian often uses the present tense for this kind of general repeated behavior.

So дети сразу просят means:

• the children immediately ask
• the children always ask right away

It is not talking about one single past event.

Дети is nominative plural here because it is the subject of просят.

• дети = children
• просят = ask

So:

дети просят = the children ask

Сразу means immediately, right away, or at once.

It emphasizes how quickly the children react:

как дети сразу просят...
= and the children immediately ask...

Without сразу, the sentence would still make sense, but it would lose that sense of instant reaction.

Because хлеб is the direct object of просят, so it appears in the accusative case.

For an inanimate masculine noun like хлеб, accusative singular looks the same as nominative singular:

• nominative: горячий хлеб
• accusative: горячий хлеб

So even though it is the object, the form does not change.

If it were a different noun or a plural/animate noun, you might see a clearer case difference.

Yes. Просить can be used in more than one way.

Common patterns include:

• просить что = to ask for something
• просить кого о чём = to ask someone for/about something
• просить кого сделать что-то = to ask someone to do something

Here we have:

дети просят горячий хлеб
= the children ask for hot bread

So the thing being requested can appear directly as the object.

Из тостера literally means from the toaster or out of the toaster.

• из = from, out of
• тостер = toaster
• из тостера = from the toaster

So горячий хлеб из тостера means bread that has just come out of the toaster.

In natural English, you might simply say toast or hot toast, but the Russian phrase is literally hot bread from the toaster.

It is understandable, but many native speakers might more naturally say something like:

• тосты
• поджаренный хлеб
• горячие тосты

That said, горячий хлеб из тостера is perfectly understandable and paints a clear picture: bread that has just been toasted and is still hot.

Russian word order is more flexible than English word order. Here the sentence begins with the trigger phrase:

Стоит мне открыть банку варенья...

This puts strong focus on the idea the moment I open the jam.

Then comes the result:

...как дети сразу просят горячий хлеб из тостера.

English also sometimes does this with fronting:

As soon as I open a jar of jam, the children immediately ask...

So although the order may feel unusual at first, it is quite normal in Russian.

Yes, very naturally.

Стоит мне только открыть банку варенья, как дети сразу просят...

This adds extra emphasis:

• all I have to do is open...
• the moment I so much as open...

It makes the sense of immediate, predictable reaction even stronger.

It sounds slightly expressive and a little playful or mildly complaining, in the sense of:

Every single time I open the jam, the kids immediately want toast.

So the construction is not just neutral timing. It often carries a feeling of:

• repeated experience
• inevitability
• mild exasperation, amusement, or emphasis

That emotional coloring is one reason this pattern is so common in everyday Russian.