När jag var barn brukade vi alltid gå till skolan tillsammans.

Yes, när can mean when in a question, but here it is not asking a question. It introduces a time clause:

• När jag var barn = When I was a child

So in this sentence, när is a subordinating conjunction meaning when.

In Swedish, after vara (to be), words for roles, identities, and life stages often appear without an article.

So:

• jag var barn = I was a child
• hon är läkare = she is a doctor
• han är student = he is a student

Using ett here is usually less natural in ordinary Swedish. Jag var ett barn is possible, but it sounds more emphatic, contrastive, or literary—more like I was a child in the sense of I was only a child.

This is because Swedish follows the V2 rule in main clauses: the finite verb must come in the second position.

Compare:

• Vi brukade alltid gå till skolan tillsammans.
• När jag var barn brukade vi alltid gå till skolan tillsammans.

In the second version, the whole clause När jag var barn takes the first position. That means the finite verb brukade must come next, before the subject vi.

So:

• first position: När jag var barn
• second position: brukade
• then subject: vi

This inversion is very common in Swedish.

Brukade expresses a habit in the past. It is often translated as:

• used to
• sometimes would (for repeated past actions)

So brukade vi gå means we used to go.

It tells you this was something that happened repeatedly, not just once.

Because they do slightly different jobs:

• brukade = this happened habitually / repeatedly
• alltid = this happened always

So together they mean something like:

• we used to always go...
• it was our regular habit to always go...

It is not redundant. Brukade gives the idea of a past routine, and alltid tells you the frequency within that routine.

Because brukade is followed by the infinitive form of the next verb.

So:

• brukade gå = used to go

Not:

• brukade gick ❌

This is similar to English used to go, not used to went.

After bruka in this meaning, Swedish normally uses the bare infinitive—that is, the infinitive without att.

So you say:

• bruka gå
• brukade gå

not normally:

• brukade att gå ❌

This is something you mainly just learn as part of the pattern:

• bruka + infinitive

In Swedish main clauses, adverbs like alltid, ofta, aldrig, and inte often come after the finite verb and the subject.

Here the pattern is:

• brukade = finite verb
• vi = subject
• alltid = adverb

So:

• När jag var barn brukade vi alltid gå...

This is standard Swedish word order.

Compare:

• Vi brukade alltid gå...
• När jag var barn brukade vi alltid gå...

The position of alltid stays natural in both.

Because till expresses movement toward a destination:

• gå till skolan = go/walk to school

But i skolan usually means being in school / at school rather than moving there.

So the difference is roughly:

• gå till skolan = go to the school / go to school physically
• vara i skolan = be at school / be in school

This sentence is about the action of going there, so till is the natural choice.

Because Swedish uses the definite form here: skolan.

This is part of the normal idiomatic expression:

• gå till skolan

Even though English says go to school without the, Swedish often uses the definite form in places where English does not use an article.

So you should not translate word-for-word here. Just learn gå till skolan as the natural Swedish phrase.

Tillsammans means together.

It is placed at the end because that is a very natural position for it in this sentence:

• ...gå till skolan tillsammans

Swedish often puts this kind of adverb later in the sentence. It can sometimes move, but the final position sounds very normal and smooth here.

Here it means child in the singular sense: when I was a child.

You are right that barn has the same form in the indefinite singular and plural:

• ett barn = a child
• två barn = two children

So you understand the number from the context. In this sentence, jag var barn clearly refers to the speaker’s childhood, so the meaning is singular.

Yes. När jag var liten is very common and natural, and it also means when I was little / when I was a child.

So these are both possible:

• När jag var barn...
• När jag var liten...

The second one is often a bit more everyday and conversational.