Vor dem Schlafen wickelt meine Frau das Baby noch einmal.

Because Schlafen is being used as a noun-like form here, not just as a normal verb.

In vor dem Schlafen, German turns the infinitive schlafen into a nominalized infinitive: das Schlafen = sleeping.

That is why it is:

• capitalized: Schlafen
• used with an article: dem
• treated like a noun grammatically

So:

• schlafen = to sleep
• das Schlafen = sleeping

German does this very often:

• beim Essen = while eating
• nach dem Lernen = after studying
• vor dem Schlafen = before sleeping

Because vor takes the dative here.

With two-way prepositions like vor, German chooses the case based on meaning:

• dative for a location or a time setting
• accusative for movement toward something

In this sentence, vor dem Schlafen means before sleeping, so it expresses time, not movement. That is why German uses the dative:

• das Schlafen → nominative
• dem Schlafen → dative

So:

• vor dem Schlafen = before sleeping

Because German is a verb-second language in main clauses.

The first element in this sentence is the time phrase:

• Vor dem Schlafen

Once that phrase takes first position, the finite verb must come second:

• Vor dem Schlafen wickelt ...

Then the subject comes after the verb:

• Vor dem Schlafen wickelt meine Frau das Baby noch einmal.

This is completely normal German word order.

Compare:

• Meine Frau wickelt das Baby noch einmal vor dem Schlafen.
• Vor dem Schlafen wickelt meine Frau das Baby noch einmal.

Both are correct. The second version gives more emphasis to the time phrase.

Because meine already works like a determiner.

In German, possessive words such as:

• mein
• dein
• sein
• ihr
• unser

usually replace the article rather than appearing with one.

So German says:

• meine Frau = my wife

not:

• die meine Frau in this kind of sentence

The possessive already carries the job that an article would normally do.

Because Baby is a neuter noun in German:

• das Baby

Also, in this sentence it is the direct object of wickelt, so it is in the accusative case. But for neuter nouns, the definite article is the same in nominative and accusative:

• nominative: das Baby
• accusative: das Baby

So the form does not change.

There are two main clues.

1. Meaning of the verb

• wickeln needs someone who does the action and someone receiving it.
• Here, meine Frau is doing the wrapping/changing, so it is the subject.
• das Baby receives the action, so it is the object.

2. Word order plus case Even though the verb comes before the subject here, German still allows that because of verb-second structure:

• Vor dem Schlafen = first element
• wickelt = finite verb in second position
• meine Frau = subject
• das Baby = direct object

If you changed the order, the meaning would usually still be clear from context and grammar:

• Meine Frau wickelt vor dem Schlafen das Baby noch einmal.

Noch einmal usually means again or one more time.

In this sentence it suggests that the wife wraps/changes the baby once more before sleeping.

Depending on context, English might translate it as:

• again
• one more time
• once again

The phrase often adds a sense of just one final extra time before something else happens.

Compare:

• Erklär das bitte noch einmal. = Please explain that again / one more time.
• Sie schaut noch einmal nach. = She checks one more time.

Often, yes.

Wickeln literally has to do with wrapping, but when used with a baby, it very commonly means:

• to change the baby
• especially to change the baby’s diaper/nappy

So in a sentence like this, many learners may see a translation such as:

• Before sleeping, my wife changes the baby one more time.

German often leaves that a bit implicit because ein Baby wickeln is a very common expression.

Yes, that is possible, but it is a slightly different structure.

• Vor dem Schlafen ... uses a prepositional phrase with a nominalized verb.
• Bevor meine Frau schläft, ... uses a subordinate clause with bevor.

Both can express a similar idea:

• Vor dem Schlafen wickelt meine Frau das Baby noch einmal.
• Bevor meine Frau schläft, wickelt sie das Baby noch einmal.

The first is often a bit more compact and idiomatic for general routines.

Also, depending on meaning, some speakers might prefer:

• Bevor meine Frau ins Bett geht, wickelt sie das Baby noch einmal.

because before sleeping in English often really means before going to bed, and German may express that more explicitly.

Yes. That is also grammatical.

German allows some flexibility in word order, especially with adverbials like time phrases.

These are all possible:

• Vor dem Schlafen wickelt meine Frau das Baby noch einmal.
• Meine Frau wickelt das Baby noch einmal vor dem Schlafen.
• Meine Frau wickelt das Baby vor dem Schlafen noch einmal.

The differences are mostly about emphasis and information focus, not basic meaning.

Putting Vor dem Schlafen first makes that time setting more prominent.

Because that is not idiomatic German.

After vor in this meaning, German normally needs either:

1. a noun phrase

• vor dem Schlafen

or

2. a full clause

• bevor sie schläft
• bevor sie ins Bett geht

A bare infinitive like vor schlafen does not work here.

So the natural options are:

• vor dem Schlafen
• bevor ...

Grammatically, the phrase itself does not explicitly say who is sleeping.

It just means before sleeping / before going to sleep. In real context, listeners usually infer who is meant.

In this sentence, many people would understand it as something like:

• before bedtime
• before someone goes to sleep

If you want to be completely explicit, German can say:

• Bevor das Baby schläft, ...
• Bevor meine Frau schlafen geht, ...
• Vor dem Schlafengehen des Babys ... (more formal/stiff)

So the original sentence is natural, but context decides whose sleep is meant.