Barnen får inte gå över gatan utan en vuxen.

Barnen is the definite plural form of barn.

• ett barn = a child
• barn = children
• barnet = the child
• barnen = the children

So barnen means the children, not just children in general.

Here, får means are allowed to or may.

The verb is få, which can mean different things depending on context:

• få = get, receive
• få + infinitive = be allowed to, get to

In this sentence, får inte gå means are not allowed to go / must not go.

So this is not about getting something; it is about permission.

Because får is the finite verb, and in a normal Swedish main clause, inte usually comes after the finite verb.

Pattern:

• Subject + finite verb + inte + rest

So:

• Barnen får inte gå ...

This is very typical Swedish word order.

Compare:

• Jag kommer inte. = I am not coming.
• Hon kan inte simma. = She cannot swim.

Because after får, Swedish uses the infinitive form of the next verb.

• får gå = may go / are allowed to go

Here:

• får is the conjugated verb
• gå stays in the infinitive

Compare:

• Jag vill gå. = I want to go.
• De måste vänta. = They must wait.

So går would be wrong here, because går is a present tense form, not an infinitive.

It means cross the street.

Literally, gå över is something like go over or walk across, but in this context the natural English meaning is cross.

So:

• gå över gatan = cross the street

This is a very common Swedish way to express crossing from one side to the other.

Gatan is the definite singular form of gata.

• en gata = a street
• gatan = the street

Swedish often uses the definite form where English uses the. So över gatan is across the street.

Utan means without.

So:

• utan en vuxen = without an adult

It introduces something that is absent. In this sentence, it means the children are not allowed to cross the street unless an adult is with them.

Because vuxen here is being used as a countable noun, meaning an adult, so Swedish normally uses the article en.

• en vuxen = an adult

So:

• utan en vuxen = without an adult

This is different from some English phrasing, where English sometimes drops the article more easily. In Swedish, keeping en here sounds natural.

Here, vuxen is functioning as a noun.

As an adjective, it means grown-up / adult:

• ett vuxet barn would not be natural, but
• en vuxen person = an adult person

But Swedish often lets adjectives stand on their own as nouns when the meaning is clear:

• en vuxen = an adult
• de vuxna = the adults

So in this sentence, en vuxen means an adult person.

Usually here it means must not or are not allowed to.

That is different from kan inte, which usually means cannot / are unable to.

Compare:

• Barnen får inte gå över gatan ... = The children are not allowed to cross the street ...
• Barnen kan inte gå över gatan ... = The children cannot cross the street ...

So får inte is about permission, not ability.

It means any adult, not one specific adult.

Because it says en vuxen, it means an adult in a general sense. So the idea is:

• not alone
• not unless an adult is with them

It does not mean one particular known adult.

It is completely natural.

It sounds like a normal rule or safety instruction, for example:

• at school
• in traffic safety advice
• in a sign or policy
• in instructions from parents or teachers

A very close English equivalent would be:

• The children must not cross the street without an adult.
• Children are not allowed to cross the street without an adult.

Both capture the Swedish well.