Børnene laver en vej i sandkassen, mens jeg venter.

Børnene means the children. Danish often makes nouns definite by adding an ending, instead of using a separate word like the.

• barn = child
• børn = children
• børnene = the children

So Børnene laver en vej... means The children are making a road/path...

That is because barn has an irregular plural:

• et barn = a child
• barnet = the child
• børn = children
• børnene = the children

This is just something you need to learn as a vocabulary pattern. It is similar to English child → children, which is also irregular.

Because vej is a common-gender noun in Danish, so it takes en in the indefinite singular.

• en vej = a road / a path
• vejen = the road / the path

In Danish, nouns are either common gender or neuter, and you have to learn which article goes with each noun.

Laver is the present tense of lave, which very often means make or do.

In this sentence, laver en vej i sandkassen means something like:

• make a road/path in the sandbox
• build a little road in the sand

Danish often uses lave in places where English might choose a more specific verb.

Yes, you could, but the nuance is a little different.

• laver en vej = making a road/path
• bygger en vej = building a road/path

In a sandbox context, laver sounds very natural, because children are just creating or shaping something in the sand. Bygger is possible, but it can sound a bit more literal or more focused on construction.

I means in, and sandkassen means the sandbox.

• en sandkasse = a sandbox
• sandkassen = the sandbox

So i sandkassen literally means in the sandbox.

Danish uses i because the children are understood to be working inside the sandbox, not on top of it in the sense of surface contact.

Danish very commonly forms compound nouns as a single word.

• sand = sand
• kasse = box
• sandkasse = sandbox

Then the definite ending is added:

• sandkassen = the sandbox

This is very normal in Danish, and English speakers often need time to get used to it.

Mens means while. It introduces a subordinate clause.

So the sentence is divided like this:

• Børnene laver en vej i sandkassen = main clause
• mens jeg venter = subordinate clause

Together: The children are making a road/path in the sandbox while I wait.

Because after mens, Danish uses normal subordinate-clause word order: subject + verb.

So:

• jeg = subject
• venter = verb

That gives mens jeg venter = while I wait

This is actually similar to English.

Yes. If the subordinate clause comes first, the main clause follows the Danish verb-second rule.

So you can say:

• Mens jeg venter, laver børnene en vej i sandkassen.

Notice that after the opening clause, the verb laver comes before the subject børnene in the main clause.

That inversion is very important in Danish main clauses.

Because Danish usually uses the simple present where English may use either the simple present or the present continuous.

• jeg venter = I wait / I am waiting
• børnene laver = the children make / are making

In this sentence, English naturally uses are making and am waiting, but Danish just uses the ordinary present tense.

It can absolutely be used for a small path or road-like shape, including one children make in a sandbox.

Depending on context, vej can mean:

• road
• street
• way
• path-like track

Here it clearly refers to a small road/path made in the sand.

Here is a simple breakdown:

• Børnene = subject
• laver = verb
• en vej = object
• i sandkassen = prepositional phrase telling where
• mens jeg venter = subordinate clause telling what happens at the same time

So the structure is:

Subject + verb + object + place + subordinate clause

A rough English-friendly approximation is something like BUR-nuh-nuh, but that is only approximate.

A few things to notice:

• ø is a vowel English does not really have
• the r affects the vowel quality
• the ending -ene is usually pronounced lightly

If you want to sound more natural, it helps to hear native audio and repeat it, because Danish pronunciation is often less obvious than the spelling suggests.

Because Danish punctuation normally uses a comma before a subordinate clause.

So in:

• Børnene laver en vej i sandkassen, mens jeg venter.

the comma marks the beginning of the clause introduced by mens.

In modern Danish, comma styles can vary a little depending on the system used, but this comma is very standard and expected.