Learn Hardcore Russian: В комнате племянника стоят игрушечные машины, и на каждой машине есть маленький номер. - In my nephew’s room there are toy cars, and on each car there is a small number.

So В комнате племянника literally means “In the room (of the nephew)”. You must change комната to its prepositional form комнате after в in this static-location meaning.

Why is it племянника after комнате? Which case is this and what does it mean?

Племянника is genitive singular of племянник (“nephew”). The genitive is used here to show possession: комната племянника = “the nephew’s room / the room of the nephew.”

Inside the phrase в комнате племянника:

в комнате – preposition + prepositional: “in the room”
племянника – genitive: “of (the) nephew”

Russian usually shows “X’s Y” as Y + genitive of X:

дом друга – “a friend’s house”
книга учителя – “the teacher’s book”
комната племянника – “the nephew’s room”

So племянника is genitive, marking whose room it is.

Can I say Игрушечные машины стоят в комнате племянника instead? Does the word order change the meaning?

Yes, Игрушечные машины стоят в комнате племянника is grammatically correct and means the same basic thing.

The difference is emphasis and information structure:

В комнате племянника стоят игрушечные машины…
The location (в комнате племянника) is put first, so it’s slightly more emphasized. It’s like starting with “In my nephew’s room, there are toy cars…”.
Игрушечные машины стоят в комнате племянника…
The subject (игрушечные машины) is first, so you’re focusing more on the toy cars, then specifying where they are.

Both are natural; Russian word order is flexible, and here the choice mostly affects what feels like the “starting point” of the sentence.

What does стоят literally mean here? Why use стоят and not just есть or находятся?

Literally, стоят is “(they) stand / are standing.” In Russian, you often choose a verb that describes the physical position of objects:

стоят – stand (upright objects, or cars parked somewhere)
лежат – lie (lying down, or objects lying horizontally)
висят – hang (on a wall, hanging from something)

In this sentence, стоят игрушечные машины implies they are standing/parked somewhere in the room (on the floor, on a shelf, etc.).

You could also say:

В комнате племянника есть игрушечные машины. – “There are toy cars in the nephew’s room.” (more neutral, existence)
…находятся игрушечные машины. – also “there are / are located,” more formal or neutral.

Стóят gives a bit more of a visual image: you see the cars “standing” there.

Why is it игрушечные машины and not something like игрушки машины? How is игрушечные formed?

In Russian, we normally express “toy X” with an adjective: игрушечный X.

игрушечная кукла – toy doll
игрушечный мишка – toy teddy bear
игрушечные машины – toy cars

Игрушечный is an adjective formed from the noun игрушка (“toy”) with the suffix -ечн-:
игрушк- + -ечн- + ый → игрушечный.

So игрушечные машины literally is “toy cars” (cars of toy type), not “toys that are cars” as two separate nouns. A phrase like игрушки машины would be ungrammatical in this meaning.

Does машины mean “cars” or “machines” here? How do Russians know which one is meant?

The word машина can mean both:

“car” (most common everyday meaning)
“machine” in a broader, technical sense (context-dependent)

In this sentence, игрушечные машины naturally reads as “toy cars,” because:

In everyday speech, машина without extra context usually means “car.”
“Toy machines” in a broad technical sense would be unusual; “toy cars” is the most plausible interpretation.

So context and real-world likelihood tell Russians that машины = “cars” here.

Why is there a comma before и: …, и на каждой машине есть маленький номер? In English we often don’t put one before “and”.

In Russian, a comma is required here because и connects two independent clauses, each with its own grammatical subject and predicate:

(В комнате племянника) стоят игрушечные машины – verb: стоят
(на каждой машине) есть маленький номер – verb: есть

Rule: when и joins two complete clauses with their own verbs, you normally put a comma before и.

In English, we often write this as one sentence without a comma (“…toy cars and on each car there is a small number”), but Russian punctuation is stricter in this case.

In на каждой машине, why is машине in that form? Which case is it, and why is it used?

Машине is prepositional singular of машина.

The preposition на takes:

accusative (куда?) when there is movement onto something:
ставить машину на улицу – “to put/drive the car onto the street”
prepositional (где?) when it describes static location “on / on top of / on the surface of”:
машина на улице – “the car is on the street”

Here, на каждой машине describes where the number is (no movement), so we use prepositional:
машина → (на) машине.

Thus на каждой машине = “on each car.”

What case is каждой in на каждой машине, and how does it agree with машине?

Каждой is feminine singular prepositional (it could also be dative in the same form, but here it’s prepositional).

It must agree with машине in:

gender: feminine (каждая, машины are feminine)
number: singular (each one car)
case: prepositional (because of на in the static “on” meaning)

Declension of каждый (each):

Nominative fem.: каждая
Prepositional fem.: о каждой / на каждой

So на каждой машине uses both words in the feminine singular prepositional.

What is the function of есть in на каждой машине есть маленький номер? Can I leave есть out?

Есть here is the existential verb “there is / there exists.”
На каждой машине есть маленький номер = “On each car there is a small number.”

In Russian, есть is often used to clearly state existence or presence, especially when introducing new information:

На столе есть книга. – “There is a book on the table.”

You can sometimes omit есть, especially in the present tense, if the context is clear:

На каждом столе книга. – “On each table (there is) a book.”

In your exact sentence, На каждой машине маленький номер is possible and still understandable. Including есть just makes the “there is” idea more explicit and sounds very natural.

Why is номер singular? In English we might think of “numbers,” because each car has its own number.

Russian treats this as “on each car there is a small number” (singular per car). The sentence is talking about the pattern:

each individual car → one individual number on it.

So grammatically:

маленький номер – nominative singular (it’s the thing that “exists” on each car)

If you wanted to emphasize plurality across all cars, you could say something like:

На машинах разные маленькие номера. – “There are different small numbers on the cars.”

But with на каждой машине есть маленький номер, the focus is “each car has a number,” so номер is singular.

Can маленький номер here mean a license plate, or only a numeric symbol painted on the toy car?

Номер is a very general word in Russian. It can mean:

a number (as a digit/printed number)
a room number
a license plate number
a serial number, etc.

For toy cars, маленький номер could naturally be:

a tiny printed number on the side (like “7”, “25”)
or a little license-plate-style number

Without extra context, Russian speakers will just picture “a small number/number sign on each toy car.” It doesn’t strictly specify whether it’s a racing number, a license plate, or some other kind of number.