Das Kinderzimmer ist noch nicht ordentlich, weil überall Bauklötze liegen.

Because Kinderzimmer is a neuter noun. In German, the gender of a compound noun is determined by the last part of the word. Here, the last part is Zimmer, and das Zimmer is neuter, so the full word is das Kinderzimmer.

Also, Kinderzimmer is a compound:

• Kinder = children
• Zimmer = room

So it literally means children’s room or kid’s room.

German often uses the plural form in compounds when something is associated with children in general. So Kinderzimmer means a room for children, not just for one child.

This is very common:

• Kinderbuch = children’s book
• Kindergarten = kindergarten
• Kinderarzt = children’s doctor / pediatrician

So Kinderzimmer is simply the standard word.

Noch nicht means not yet.

It is made up of:

• noch = still / yet
• nicht = not

Together, they express that something is currently not the case, but it may become true later.

So:

• Das Kinderzimmer ist noch nicht ordentlich = The children’s room is not tidy yet

If you said only nicht ordentlich, that would just mean not tidy, without the extra idea of yet.

Here, ordentlich means tidy, neat, or in order.

In other contexts, ordentlich can also mean things like:

• proper
• decent
• organized

But in a sentence about a room, ordentlich most naturally means tidy.

So Das Kinderzimmer ist noch nicht ordentlich means the room is still messy or not properly put in order.

Because weil is a subordinating conjunction. In German, a subordinate clause introduced by weil sends the conjugated verb to the end of the clause.

So:

• main clause: Das Kinderzimmer ist noch nicht ordentlich
• subordinate clause: weil überall Bauklötze liegen

This is a very important pattern:

• ..., weil ich müde bin.
• ..., weil er heute arbeitet.
• ..., weil überall Bauklötze liegen.

In English, word order usually stays more normal after because, but in German, weil changes the word order.

German often uses position verbs where English would simply use to be.

Liegen means to lie or to be lying. It is used for things that are in a horizontal position or scattered on a surface.

So:

• Überall Bauklötze liegen = building blocks are lying everywhere

This sounds more natural in German than just using sein.

Compare:

• Das Buch liegt auf dem Tisch. = The book is on the table.
• Die Kinder liegen im Bett. = The children are lying in bed.

German prefers these more specific location verbs:

• liegen = lie
• stehen = stand
• sitzen = sit

Bauklötze is the correct plural of der Bauklotz.

Singular:

• der Bauklotz = building block

Plural:

• die Bauklötze = building blocks

The plural is formed with:

• an umlaut change: o → ö
• the ending -e

This kind of plural pattern is very common in German.

Because Bauklötze is plural, the verb is also plural:

• Bauklötze liegen

Überall means everywhere.

In this sentence, it tells you where the building blocks are:

• weil überall Bauklötze liegen = because building blocks are lying everywhere

German word order is a bit flexible, so you may also see similar variations in other contexts, but this version is very natural.

The emphasis here is that the blocks are scattered all over the room, which explains why it is not tidy.

In a normal German main clause, the conjugated verb usually comes in second position. This is often called the V2 rule.

So in:

• Das Kinderzimmer ist noch nicht ordentlich

the subject Das Kinderzimmer comes first, and the finite verb ist comes second.

That is standard main-clause word order in German.

Then after weil, the sentence switches to subordinate-clause word order, where the verb goes to the end:

• ..., weil überall Bauklötze liegen.

Yes, but the word order changes.

With weil, the verb goes to the end:

• Das Kinderzimmer ist noch nicht ordentlich, weil überall Bauklötze liegen.

With denn, the clause keeps normal main-clause word order:

• Das Kinderzimmer ist noch nicht ordentlich, denn überall liegen Bauklötze.

Both can mean because, but they are not used exactly the same way:

• weil is a subordinating conjunction
• denn is a coordinating conjunction

In everyday German, weil is very common.

There is a comma before weil:

• Das Kinderzimmer ist noch nicht ordentlich, weil überall Bauklötze liegen.

In German, subordinate clauses introduced by words like weil, dass, wenn, and obwohl are normally separated from the main clause by a comma.

So the comma is required here.

It is functioning as an adjective here.

In:

• Das Kinderzimmer ist noch nicht ordentlich

ordentlich describes the noun Kinderzimmer, linked by the verb ist. This is called predicate adjective use. In German, predicate adjectives are not inflected, so you just get the basic form ordentlich.

Compare:

• ein ordentliches Kinderzimmer = a tidy children’s room
  
  • here the adjective is before the noun, so it takes an ending
• Das Kinderzimmer ist ordentlich = the children’s room is tidy
  
  • here it comes after ist, so no ending

Yes. In many cases, liegen is best understood as to be lying or to be situated rather than as a dramatic physical action.

Here it does not mean the blocks intentionally lie down. It just means they are there, scattered around in a lying position.

So a natural interpretation is:

• there are building blocks lying everywhere or
• building blocks are all over the place

German often uses these posture/location verbs in a way that sounds stronger or more specific than English.