Barna tar på seg hver sin pyjamas og finner hver sine tøfler ved døren.

Barna means the children. It is the definite plural form of barn.

A useful thing to remember:

• et barn = a child
• barn = children
• barna = the children

So barna is not just children in general, but the children.

Å ta på seg means to put on clothes.

It is a reflexive expression:

• ta på = put on
• seg = oneself / himself / herself / themselves

So barna tar på seg means the children put on something on themselves.

In Norwegian, this reflexive form is very common with clothes:

• Hun tar på seg jakka. = She puts on her jacket.
• De tar på seg skoene. = They put on their shoes.

Also, seg is used for third person reflexive whether the subject is singular or plural, so it can refer to he/she or they.

Hver sin pyjamas means each their own pajamas or more naturally a pajama set each.

This is a very common Norwegian pattern:

• hver = each
• sin = his/her/their own

So the idea is not that the children share one set of pajamas. It means that each child has a separate one.

A very literal breakdown would be:

• hver sin pyjamas = each [one] his/her own pajamas

In natural English, we usually rephrase it rather than translate word for word.

Because sin/si/sitt/sine must agree with the thing being owned, not with the owner.

Here:

• pyjamas is singular → sin pyjamas
• tøfler is plural → sine tøfler

The full set is:

• sin = singular common gender
• si = singular feminine
• sitt = singular neuter
• sine = plural

So the sentence uses:

• hver sin pyjamas
• hver sine tøfler

because pyjamas is singular, while tøfler is plural.

Because hver tells you the meaning is one set per person, but sine still has to match the noun tøfler, which is plural.

So:

• hver = each child individually
• sine tøfler = his/her own slippers

This is completely normal in Norwegian. Compare:

• hver sin bok = a book each
• hver sitt rom = a room each
• hver sine sko = their own shoes each

Even though hver is singular in meaning, the possessed noun can still be plural.

Because when a possessive comes before the noun, Norwegian normally uses the indefinite noun form.

So you get:

• sin pyjamas
• sine tøfler

not:

• sin pyjamasen
• sine tøflene

Compare the two patterns:

• sin pyjamas = his/her own pajamas

• pyjamasen sin = his/her pajamas

• sine tøfler = his/her own slippers
• tøflene sine = his/her slippers

Both patterns exist, but with hver sin / hver sine, the noun is normally indefinite.

Because sin/si/sitt/sine is the reflexive possessive, used when the owner is the same as the subject of the clause.

Here, the subject is barna, and the pajamas/slippers belong to those same children. So Norwegian naturally uses sin/sine.

• Barna tar på seg hver sin pyjamas.
• Barna finner hver sine tøfler.

If you used deres, it would sound less natural here and could suggest a more external or less clearly reflexive relationship.

Also, hver sin / hver sine strongly emphasizes one each. That is exactly the meaning needed in this sentence.

In Norwegian, pyjamas is usually treated as one item: one pajama set.

So:

• en pyjamas = one set of pajamas

But tøfler means slippers, and slippers normally come as two separate items, so Norwegian often uses the plural:

• tøfler = slippers

So the sentence is saying that each child puts on:

• one pajama set
• their own slippers

This is why the forms are different.

Ved døren means by the door or at the door.

It tells you the slippers are located near the door.

• ved = by / near / at
• døren = the door

So ved døren is a location phrase.

A learner might also see ved døra. That means the same thing. In Bokmål, both døren and døra are possible definite forms of dør.

Yes, that would also be grammatical, but the meaning changes slightly.

• pyjamasene sine / tøflene sine = their pajamas / their slippers
• hver sin pyjamas / hver sine tøfler = one each, their own individual ones

So hver adds a clear distributive meaning: each child has a separate pajama set and separate slippers.

Without hver, the sentence is still fine, but it does not emphasize one each as strongly.