Når børneværelset er ryddeligt, kan babyen kravle frit mellem sengen og døren.

Når usually means when in the sense of a real, expected, repeated, or general situation.

So Når børneværelset er ryddeligt ... means something like:

• When the nursery/the children’s room is tidy ...
• or Whenever the nursery is tidy ...

By contrast, Hvis means if and often sounds more hypothetical or uncertain.

• Når børneværelset er ryddeligt, kan babyen kravle frit ...
  = This is presented as a normal condition.
• Hvis børneværelset er ryddeligt, kan babyen kravle frit ...
  = This sounds more like a possibility: if it happens to be tidy.

Both can be grammatical in many contexts, but the nuance is different.

This is because Danish main clauses follow the V2 rule: the finite verb normally comes in the second position.

Here, the whole Når-clause comes first:

• Når børneværelset er ryddeligt = first element

So the finite verb in the main clause must come next:

• kan = second position
• babyen = subject after the verb

That is why you get:

• Når børneværelset er ryddeligt, kan babyen kravle frit ...

If you put the main clause first, the order changes back to the more familiar pattern:

• Babyen kan kravle frit mellem sengen og døren, når børneværelset er ryddeligt.

Because Danish, like German, usually writes compound nouns as one word.

børneværelset can be broken down like this:

• børne- = child/children
• værelse = room
• -et = the definite ending for a neuter noun

So:

• et børneværelse = a children’s room / a nursery
• børneværelset = the children’s room / the nursery

English often writes this as two words, but Danish normally combines it into one.

Because værelse is a neuter noun:

• et værelse = a room

When an adjective describes a singular neuter noun, it often takes -t:

• et stort værelse = a big room
• værelset er stort = the room is big

The same happens here:

• ryddelig → ryddeligt

So:

• børneværelset er ryddeligt = the nursery/the children’s room is tidy

Here ryddeligt means tidy, neat, or cleared up.

It suggests that things have been put away and the room is orderly enough for the baby to move around safely.

It is not exactly the same as clean in the sense of washed or spotless. For that, Danish often uses rent:

• ryddeligt = tidy, uncluttered
• rent = clean

So in this sentence, the focus is more on the room being free of mess than on it being freshly cleaned.

Because babyen is the definite form:

• en baby = a baby
• babyen = the baby

Danish usually puts the definite article at the end of the noun instead of using a separate word like English the.

In this sentence, babyen probably refers to a specific baby already known from the context.

Because after a modal verb such as kan, Danish uses the infinitive without at.

So:

• kan kravle = can crawl
• not kan at kravle

This is similar to English:

• can crawl
• not can to crawl

Other common modal verbs work the same way:

• skal gå = must/will go
• vil spise = wants to / will eat
• må komme = may / must come

Because frit is functioning as an adverb here: it describes how the baby crawls.

• fri = free (adjective)
• frit = freely / in a free way (adverb or neuter form)

So:

• babyen kan kravle frit = the baby can crawl freely

A useful comparison:

• en fri person = a free person
• personen kan bevæge sig frit = the person can move freely

Because in Danish, the normal way to say the bed and the door is with the definite ending on the noun:

• sengen = the bed
• døren = the door

Using den before the noun is usually for special cases, especially:

1. with an adjective

   • den store seng = the big bed

2. for emphasis or contrast

   • ikke den seng, men den anden seng = not that bed, but the other bed

So in a simple phrase like this, sengen and døren are the normal forms.

Yes.

You can say:

• Når børneværelset er ryddeligt, kan babyen kravle frit mellem sengen og døren.

Or:

• Babyen kan kravle frit mellem sengen og døren, når børneværelset er ryddeligt.

Both are natural. The difference is mostly about focus and style:

• starting with Når ... highlights the condition first
• starting with Babyen ... highlights the baby and the action first

The word order in the main clause changes accordingly because of the Danish V2 rule.

Not always. Mellem can mean between, and in many contexts it can also cover what English might call among.

In this sentence, it clearly means between, because there are two things:

• mellem sengen og døren = between the bed and the door

But Danish also uses mellem in broader situations, for example with several objects or people. So its range is a bit wider than English between in everyday use.