Recently I watched a documentary about the causes of childrens getting involved in crime.

Children is already the plural of child

ThisIt reports a series of key factors that explain why they tend to commit criminal actions even inat an early age into the teenager's aglife.

It sounds better than This in this scenario, though can't explain exactly why. Not grammatically incorrect though.

At should be used, weird preposition things

Teenagers needs apostrophe

While also not grammatically incorrect, saying "early age into the teenager's age" sounds off, I'd say teenager's life in this case

First of all, there is a main and unavoidable topic at these ages in all the cases that were shown, that is, the social context: they live in the outskirts, in poor neighbourhoods where the unemployment makes it unthinkable for them being able to think inonabout a better future.

You need "it" to show what is being made unthinkable
Inon isn't a preposition, I'd use about

Such is the case of Kevin, who at the age of 10 spent most of his time alone and out of school, looking into the garbage for something to eat.

Preposition "for" is needed

So by far, we could imagine his parents cando not afford all the material necessary for a proper education.

Cando isn't a word

What it was described above link in some sense toreinforces the firsthand view of a social worker in the film, who stated that it is not a matter of surprise the relationship between desperation of young children and bad actions like crime isn't a surprise.

Rephrasing

You don't say a matter of surprise, just surprise, also moved "isn't a surprise" to describe the relationship

Secondly, this example may just shows the lack of parental control and discipline.

Incorrect conjugation

SThis was a statement which was firmly expressed forby one of the experts interviewed.

You never stated what the statement is, you need to explain what it is

Wrong preposition

Nonetheless, in my humble opinion, it was not taken into account that covering basics needs is prior tomore important than anything else, even a firm morals which took Kevin out of thisese kinds of problems.

Using "prior" sounds weird here
Adjectives aren't plural

Note that if Kevin didn't recover, you'd use "which could have took Kevin" instead of "which took"

OIn summary, in some areas the social elevator haves never worked as it is expected, and this phenomenon affects influences to differents generations, a reason why parents may not assure the typical educational and moral rules which are supposed to youngsare supposed to be applied young people and teenagers are applied.

It's "in summary"
You combined past and present tense, but "it is" is also unneeded in that sentence

"Affect influences" sounds odd, I'd just use "influences" as a verb

Adjectives aren't plural

Article needed

"to be applied" needs to be added, and to not make it an incomplete thought add "are applied" to the end

Youngs isn't a word

Essay CAE C1 "Crime and yYoungth in pPoor aAreas"

Recently, I watched a documentary about the causes of childrens gett becoming involved in crime.

Seeing as this is an essay, I would consider using a more formal tone, which is why I would replace "getting" with "becoming".

ThisIt reports a series of key factors that explain why they tend to commit criminal actions even infrom an early age, and into their teenagers age years.

First of all, there is a maincentral and unavoidable topicfactor at these ages inthat remained consistent throughout all of the cases that were shown,presented by the documentary; that is, the social context: they live ion the outskirts, in poor neighbourhoods where the unemployment makes it unthinkable for them beingto be able to think inonimagine a better future.

You mention "key factors" in your previous sentence, so I would choose to continue that thought and be consistent throughout here.
Also--outskirts of what? A city? A town? Specify.
You use "unthinkable" and then "to be able to think of", so I would choose to switch up the word choice here.

ObviouslyFor many children, this phenomenon starts at school.

The usage of "obviously" here seems a bit off-putting; too assertive for an introductory statement.

Such is the case ofor Kevin, who at the age of 10, spent most of his time alone and out of school and alone, looking into thethrough garbage for something to eat.

So by far, wThrough his example, one could imagine that his parents cando not afford all the materials necessary for a proper education.

I'm not quite sure if you are allowed to use personal pronouns as this is an essay, so changing "we" to "one" is up to you.

What it was describedKevin's situation above links, in some sense, to the firsthand viewperspective of a social worker in the filmdocumentary, who stated that it is not a matter of surprise thesurprising that there is a relationship between the desperation of young children and badnegative actions like crime.

SecondlyHowever, this example may justsimply shows the lack of parental control and discipline.

SThis statement which was firmly expressed forby one of the experts interviewed.

Nonetheless, in my humble opinion, it wasthe expert did not taken into account that covering basics needs is prior tonecessary before considering anything else, --even a firm moral compass--which took Kevin out of this kind of problems.

OIn summary, in some areas, the social elevator haves never worked as it is expected, and t. This phenomenon affects influences to differents generations, which is the reason why parents may not asbe able to ensure the typical educational and moral rules which are supposdevelopment which is expected tof youngsth and teenagers.

Essay CAE C1 "Crime and yYoungth in pPoor aAreas"

Recently I watched a documentary about the causes ofor why childrens getting involved inwith crime.

This reportsIt provided a series of key factors that explain why they tend to commit criminal actions even inat an early age and then into the teenagers age years.

First of all, there is athe main and unavoidable topic that occurred at these ages in all the cases that were shown, thaand it is, the social context: they live in the outskirts, in poor neighbourhoods where the unemployment makes it unthinkable for them being able to think inonabout a better future.

Obviously, tThis phenomenon starts at school.

Such is the case of Kevin, who at the age of 10 spent most of his time alone and out of school, looking into the garbage for something to eat.

So by far, we couldWe can then imagine that his parents candoould not afford all the material necessary for a proper education.

This sentence should be past tense.

What it was described above link in some sense to theThe description in the above link was a firsthand view ofrom a social worker interviewed in the film, who stated that it is not a matter of surprise theat there exists a relationship between the desperation of young children and bad actions like crime.

Secondly, this example may just showsdemonstrate the lack of parental control and discipline.

SThis statement which was firmly expressed forby one of the experts interviewed.

Nonetheless, in my humble opinion, it was not taken into account that covering basics needs is prior to anything else, even a firm moral which took Kevin out of this kind of problemstantamount.

I don't know what you mean by "even a firm moral which took Kevin out of this kind of problems" so I deleted it.

OIn summary, in some areas the social elevator haves never worked as it is expected, and this phenomenon affects influences to differents generations, which perpetuates reasons why parents may not assure the typical educational and moral rules which are supposed to youngsbe taught to children and teenagers.