Børnene leger ovenpå.

Because the noun barn has an irregular plural.

• singular indefinite: et barn = a child
• plural indefinite: børn = children
• plural definite: børnene = the children

So -ene is the definite plural ending, but it attaches to the plural form børn, not to the singular barn.

In Danish, definiteness is often added as an ending on the noun instead of using a separate word.

So:

• børn = children
• børnene = the children

This is very common in Danish. English uses a separate article, but Danish often uses a suffix.

Leger is the present tense of at lege.

• at lege = to play
• leger = play / are playing

In Danish, the present tense is often formed by adding -r to the infinitive:

• at lege → leger
• at bo → bor
• at spise → spiser

So Børnene leger ovenpå is a present-tense sentence.

Danish usually uses lege when children are playing in the general sense: playing, having fun, playing pretend, messing around.

Spille is more often used for:

• playing a game
• playing music
• playing a sport in some contexts

So Børnene leger ovenpå sounds natural for The children are playing upstairs.

Ovenpå means upstairs, on the floor above, or sometimes on top depending on context.

In this sentence, it most naturally means upstairs.

It is an adverb of place, telling you where the action happens:

• Børnene leger = The children are playing
• ovenpå = upstairs

Because in modern Danish, ovenpå is normally written as a single word when it functions as an adverb.

It is a fixed expression meaning something like upstairs/on top. Danish often joins these kinds of elements into one word.

This is the normal word order for a main clause in Danish:

subject + verb + other information

So:

• Børnene = subject
• leger = verb
• ovenpå = adverbial of place

This matches a basic English pattern: The children are playing upstairs.

Yes, that is possible in Danish.

Danish is a V2 language, which means the finite verb usually comes in the second position in a main clause. If you move ovenpå to the front for emphasis, the verb still stays second:

• Børnene leger ovenpå.
• Ovenpå leger børnene.

The second version is less neutral and puts more focus on upstairs.

A rough guide is BUR-ne-ne, but the vowel ø does not exist in standard English, so that spelling is only approximate.

A few helpful points:

• ø is a rounded front vowel
• børn sounds somewhat like burn, but with rounded lips
• -ene is usually pronounced lightly, not with a strong stress

The main stress is on børn.

A rough English-friendly guide is LYE-er or LAI-er, but again that is only approximate.

Important things to notice:

• the g is not pronounced like a hard English g in go
• the word is usually pronounced smoothly, almost like two syllables flowing together

The exact sound varies a little depending on accent and speaking speed.

Børnene is completely normal and natural in everyday Danish.

Danish does not usually drop the subject the way some languages do, so a full sentence like Børnene leger ovenpå is standard and idiomatic.

A speaker might shorten it only if the context is already very clear, but the sentence itself is perfectly ordinary.

Sometimes yes, depending on context.

Besides the literal sense upstairs/on top, ovenpå can also appear in more abstract expressions. But in a simple sentence like Børnene leger ovenpå, the natural interpretation is physical location: the children are upstairs.