Das Baby krabbelt auf dem Teppich im Wohnzimmer.

Because Baby is a neuter noun in German, so its basic article is das.

• das Baby = the baby
• ein Baby = a baby

In this sentence, das Baby is also the subject, so it is in the nominative case. For a neuter noun in nominative singular, the definite article is das.

Krabbeln is the infinitive: to crawl.

In the sentence, the subject is das Baby, which is third person singular (it), so the verb has to be conjugated:

• ich krabble
• du krabbelst
• er/sie/es krabbelt
• wir krabbeln
• ihr krabbelt
• sie/Sie krabbeln

So das Baby krabbelt means the baby crawls / is crawling.

German main clauses usually follow the V2 rule: the finite verb goes in the second position.

Here the sentence is:

Das Baby | krabbelt | auf dem Teppich im Wohnzimmer.

• Position 1: Das Baby
• Position 2: krabbelt
• Then the rest of the sentence follows.

This is one of the most important basic word-order rules in German.

Because auf is a two-way preposition. It can take:

• dative for location: where something is happening
• accusative for direction/movement toward a destination

Here, the baby is crawling on the carpet as a location, not crawling onto the carpet as a destination. So German uses the dative:

• auf dem Teppich = on the carpet

Compare:

• Das Baby krabbelt auf dem Teppich. = The baby is crawling on the carpet.
• Das Baby krabbelt auf den Teppich. = The baby crawls onto the carpet.

Because Teppich is a masculine noun: der Teppich.

After auf with a location meaning, you need the dative case. The dative singular article for a masculine noun is dem:

• nominative: der Teppich
• dative: dem Teppich

So:

• auf dem Teppich = on the carpet

Im is a very common contraction of in dem.

• in dem Wohnzimmer → im Wohnzimmer

So im Wohnzimmer literally comes from in the living room.

This contraction is standard and very common in everyday German.

Because in is also a two-way preposition, just like auf.

Here it describes location: the carpet / crawling is in the living room, so German uses the dative:

• im Wohnzimmer = in the living room

If it were about movement into the room, you would use the accusative:

• Das Baby krabbelt ins Wohnzimmer. = The baby crawls into the living room.

In practice, it works naturally with the whole scene and can also be understood as specifying where the carpet is.

So the sentence suggests:

• the baby is crawling on the carpet
• and this is happening in the living room

German often allows this kind of compact phrasing without needing to spell out every connection separately.

If you wanted to make the structure clearer, you could also say:

• Das Baby krabbelt im Wohnzimmer auf dem Teppich.

That version makes the location of the action feel a bit more explicit.

Yes. That is also correct.

Both are natural:

• Das Baby krabbelt auf dem Teppich im Wohnzimmer.
• Das Baby krabbelt im Wohnzimmer auf dem Teppich.

The difference is mostly about focus:

• auf dem Teppich im Wohnzimmer puts the carpet first, then adds where it is
• im Wohnzimmer auf dem Teppich puts the room first, then the more specific location

German word order is flexible, but the verb still stays in second position in a main clause.

Because in German, all nouns are capitalized.

So here:

• Baby = noun
• Teppich = noun
• Wohnzimmer = noun

This is a standard rule in German spelling and one of the easiest visual clues for spotting nouns.

German simple present often covers both ideas that English separates:

• The baby crawls
• The baby is crawling

So Das Baby krabbelt can mean either one, depending on context.

German does have ways to emphasize an ongoing action, but in normal everyday speech the simple present is usually enough.

There actually is one — it is hidden inside im.

• im = in dem
• and dem is the dative form of the for a neuter or masculine noun

Since Wohnzimmer is neuter (das Wohnzimmer), the dative form is dem Wohnzimmer, and after contraction:

• im Wohnzimmer = in the living room

Wohnzimmer is a compound noun, which is very common in German.

It is made from:

• wohnen = to live
• Zimmer = room

So Wohnzimmer literally means something like living room. The final part of a German compound usually determines the gender, and Zimmer is neuter (das Zimmer), so:

• das Wohnzimmer

That is why you get:

• nominative: das Wohnzimmer
• dative: dem Wohnzimmer
• contracted with in: im Wohnzimmer