На пирожном была шоколадная посыпка, и дети сразу захотели ещё.

Because на takes different cases depending on meaning:

• на + Prepositional = location, on something
• на + Accusative = motion onto something

Here the sprinkles are already on the pastry, so this is location: на пирожном.

Also, пирожное declines like an adjective, not like a typical neuter noun:

• Nominative: пирожное
• Prepositional: на пирожном

So на пирожном means on the pastry / on the little cake.

Because the grammatical subject is шоколадная посыпка.

Russian past-tense verbs agree with the subject in gender and number:

• был = masculine singular
• была = feminine singular
• было = neuter singular
• были = plural

Since посыпка is feminine singular, the verb is была.

Even though на пирожном comes first, it is not the subject. It is just the location phrase.

Because it is still the subject of the sentence.

Russian word order is much freer than English word order. The sentence is structured like this:

• На пирожном = location / setting
• была = was
• шоколадная посыпка = the thing that existed there

So this is a very natural Russian way to say something like There was chocolate topping on the pastry.

The noun посыпка is nominative because it is the subject, and the adjective шоколадная matches it in:

• gender: feminine
• number: singular
• case: nominative

Yes. Very much so.

Russian often expresses there is / there was by putting the place first and then using быть:

• На столе была книга = There was a book on the table
• В комнате были дети = There were children in the room
• На пирожном была шоколадная посыпка = There was chocolate topping on the pastry

This structure introduces something as part of the scene.

If you said Шоколадная посыпка была на пирожном, that would sound more like you are focusing specifically on the chocolate topping as the topic.

Because Russian посыпка is often used as a collective or mass noun.

English commonly uses the plural sprinkles, but Russian often treats this idea as a single substance or topping:

• шоколадная посыпка = chocolate sprinkles / chocolate topping / chocolate sprinkle coating

So even if English uses a plural noun, Russian may use a singular noun for the same idea.

This is about verbal aspect and meaning.

• хотели = wanted / were wanting
• захотели = started to want, suddenly wanted, felt like

In this sentence, захотели fits better because the children reacted at once when they saw the pastry. It suggests the desire appeared immediately.

That also matches сразу very well:

• дети сразу захотели ещё = the children immediately wanted more

If you used хотели, it would sound more like a state or background description, not such a sudden reaction.

Because it agrees with дети, which is plural.

In the past tense, Russian verbs show number, and in the singular they also show gender. Since дети means children, the verb must be plural:

• ребёнок захотел = the child wanted
• дети захотели = the children wanted

Сразу means immediately, right away, or at once.

Placed before захотели, it naturally modifies the action:

• дети сразу захотели ещё = the children immediately wanted more

This is a very normal word order. Russian can move adverbs around more than English can, but this placement is neutral and natural.

Here ещё means more or another one / some more.

This word is very common and can have several meanings depending on context:

• still: он ещё спит = he is still sleeping
• again / another: ещё раз = once more
• more: хочу ещё = I want more

In this sentence, it clearly means more.

Because Russian often leaves out a word if it is obvious from the context.

So дети сразу захотели ещё literally just says the children immediately wanted more, and the listener understands more of the pastry, more dessert, or another one from the situation.

If you wanted to say it more explicitly, you could add a noun, for example:

• дети сразу захотели ещё пирожных = the children immediately wanted more pastries
• дети сразу захотели ещё одно пирожное = the children immediately wanted one more pastry

Without the noun, the sentence sounds natural and idiomatic.

Because и is joining two full clauses:

1. На пирожном была шоколадная посыпка
2. дети сразу захотели ещё

Each part has its own predicate, so Russian normally uses a comma between them.

This is similar to English when two independent clauses are connected, although Russian punctuation rules are often stricter about this.