Barnet lader som om, bamsen sover i højstolen ved bordet.

Because barnet means the child, while barn means child in a more general or indefinite sense.

• et barn = a child
• barnet = the child

Barn is a neuter noun, so the definite singular ending is -et.

Lader som om is an idiomatic expression meaning pretends or acts as if.

So:

• Barnet lader som om ... = The child pretends ...
• more literally: The child acts as if ...

It is best to learn lader som om as a set phrase, rather than translating each word separately.

The comma is there because bamsen sover i højstolen ved bordet is a subordinate clause after som om.

In modern Danish, this comma is often optional, depending on the comma style being used.

So you may see both:

• Barnet lader som om, bamsen sover ...
• Barnet lader som om bamsen sover ...

Both can be correct.

Because after som om, Danish normally uses subordinate clause word order, where the subject comes before the verb:

• bamsen sover = the teddy bear sleeps/is sleeping

This is different from Danish main clauses, which often follow the V2 rule and can put the verb earlier.

So here the normal order is:

• som om bamsen sover

not

• som om sover bamsen

Bamsen means the teddy bear or the stuffed animal.

It comes from:

• en bamse = a teddy bear / soft toy
• bamsen = the teddy bear / the soft toy

In everyday Danish, bamse is very common for a child’s stuffed toy.

Because in Danish, you often say someone or something is in a chair, seat, or similar container-like place.

So:

• i højstolen = in the high chair

This is natural Danish usage. English often says in the high chair too, so this matches quite well.

Also:

• en højstol = a high chair
• højstolen = the high chair

Ved bordet means at the table or by the table.

• ved = by / at
• bordet = the table

So i højstolen ved bordet means the teddy bear is in the high chair, located by the table.

It does not mean the teddy bear is on the table. That would be på bordet.

Yes, you may also hear or see som om at:

• Barnet lader som om, at bamsen sover ...

But in many cases, the at is simply left out, as in your sentence. The version without at is very common and natural.

So both are possible, but:

• som om bamsen sover ... is very normal
• som om at bamsen sover ... is also possible

Because Danish often uses the present tense in exactly this kind of sentence when describing what someone is pretending right now.

• sover = sleeps / is sleeping

Danish does not have a separate progressive form like English is sleeping, so the present tense covers both ideas depending on context.

So bamsen sover can mean:

• the teddy bear sleeps
• the teddy bear is sleeping

Here, the natural meaning is is sleeping.