Learn Hardcore Norwegian: Barna ser på seg selv i speilet. - The children look at themselves in the mirror.

In Norwegian, å se på is often used for to look at, while å se alone is more like to see (perceive with the eyes, often more passive).

Barna ser på seg selv i speilet.
= The children are looking at themselves in the mirror.

If you say:

Barna ser seg selv i speilet.

this is also possible and will usually be understood as look at, but many speakers prefer se på when someone is actively directing their gaze at something.

So se på emphasizes the deliberate act of looking, not just passively seeing.

What is the function of seg here, and why not dem?

Seg is the 3rd person reflexive pronoun in Norwegian. It is used when the object refers back to the subject.

Subject: Barna (they, the children)
Object (reflexive): seg = themselves

Norwegian does not change the reflexive pronoun for singular vs plural in 3rd person:

Han ser på seg. = He looks at himself.
Hun ser på seg. = She looks at herself.
Barna ser på seg. = The children look at themselves.

Dem is the non‑reflexive object pronoun (them), used when the object is a different group/person:

Jeg ser på dem. = I look at them.
Barna ser på dem. = The children look at them (some other people).

In Barna ser på seg selv i speilet, the children are looking at themselves, so you must use seg, not dem.

Why do we have both seg and selv? What is the role of selv?

Seg is the reflexive pronoun.

Selv literally means self, and together seg selv is a more explicit or emphatic reflexive form: themselves.

seg = himself / herself / itself / themselves (depending on context)
seg selv = himself / herself / itself / themselves, often with more emphasis or clarity

In many sentences, Norwegian can use seg alone or seg selv:

Han barberer seg.
Han barberer seg selv.

Both are acceptable. Seg selv can sound a bit more emphatic or careful, like himself, not someone else.

In Barna ser på seg selv i speilet, seg selv simply reinforces that they are looking at themselves, not at other people. Barna ser på seg i speilet is also grammatical and would normally be understood the same way.

If seg selv can be dropped, is Barna ser på seg i speilet equally natural?

Yes, Barna ser på seg i speilet is grammatically correct and understandable. Many speakers would accept it without hesitation.

Nuance:

Barna ser på seg i speilet.
Neutral, quite natural.
Barna ser på seg selv i speilet.
Slightly more explicit or emphatic; for learners this form often feels clearer, because it closely matches English themselves.

In spoken language, you will hear both. In written language, seg selv is also very common when you want to avoid any ambiguity.

What tense is ser, and how does it compare to English?

Ser is the present tense of å se (to see / to look). Norwegian present tense covers both:

English simple present: The children look at themselves
English present progressive: The children are looking at themselves

So:

Barna ser på seg selv i speilet.
can be translated as either The children look at themselves in the mirror or The children are looking at themselves in the mirror, depending on context. Norwegian does not need a separate -ing form here.

Why is it i speilet and not på speilet?

Prepositions are often idiomatic. With mirrors, English says in the mirror and Norwegian also uses i (in) for this meaning:

i speilet = in the mirror (in the mirror’s reflection)

På speilet would literally be on the mirror and would usually refer to something physically on the surface of the mirror, for example:

Det er støv på speilet. = There is dust on the mirror.

So for looking at your reflection, it’s i speilet, not på speilet.

What is the grammatical form of speilet, and how is it built?

The noun is et speil (a mirror), which is a neuter noun.

Forms:

Indefinite singular: et speil = a mirror
Definite singular: speilet = the mirror
Indefinite plural: speil = mirrors
Definite plural: speilene = the mirrors

In the sentence Barna ser på seg selv i speilet, we have speilet = the mirror (definite singular), because they are looking in the mirror, not just a mirror.

How would the sentence change if it was only one child instead of several?

For one child, you would normally use barnet (the child) as the subject:

Barnet ser på seg selv i speilet.
= The child is looking at itself / himself / herself in the mirror.

Grammar:

Barnet = the child (definite singular)
The reflexive is still seg (selv) in the 3rd person, so this part does not change:
- Barna ser på seg selv ... (the children)
- Barnet ser på seg selv ... (the child)

Can you break down who is doing what in this sentence (subject, object, etc.)?

Yes:

Barna = Subject (who is doing the action)
ser på = Verb phrase (se på in infinitive) meaning look at
seg selv = Reflexive object (who they are looking at – themselves)
i speilet = Prepositional phrase (location: where they are looking)

So structurally:

Subject: Barna
Verb: ser på
Object: seg selv
Adverbial (place): i speilet

Is barna more like children or kids in tone?

Barna is neutral in tone, like standard the children in English. It can refer to:

your own children
children in general in a specific group
any group of children in context

For a more colloquial or slightly more informal/natural word in some dialects, people may also say ungene (the kids):

Ungene ser på seg selv i speilet.

But barna is very normal, neutral, and works in all registers (spoken and written).

Could the word order be changed, for example to Barna ser i speilet på seg selv?

In theory, Norwegian word order is fairly flexible, but not every possible order sounds natural.

Barna ser på seg selv i speilet.
is the natural, default order.
Barna ser i speilet på seg selv.
is technically possible but sounds unusual or awkward. Norwegian typically keeps se på together, and i speilet naturally follows as a place phrase.

So you should keep ser på seg selv together and then add i speilet at the end, as in the original sentence.