I'll give a shot at it for you. Please remember that I am not a teacher by any means, but I am a university student.
This sentence reads wrong to me because I do not think that you can count information. Buy using the word 'many', it needs to be assumed that the subject in question is able to be counted. In this situation I believe that you should be using the word 'much'. You will also need to change the word 'go' to 'goes', or 'can go'. I prefer 'can go' because it allows for the flexibility of potential.In my opinion, material on internet should be censored or controlled because many of this information go around without any kind of control.
Although 'informational content' is technically a correct statement (adj. informational, n. content), I believe that it is a rather awkward way of putting things. To be quite honest, I've never even come across the word 'informational' before, and I had trouble finding it in dictionaries. You could leave this as is, but my personal preference would be to simply use 'some internet content'. The reason why I substituted 'sometimes' with 'some' is because sometimes is used to reference time. The definition of sometimes is on occasion. I believe that to pair this word with internet content is incorrect because you would implying that one day the content is bad, other days it isn't. But it's not as though one day all of the pages on the internet are completely clean, so it's not a time issue, but an issue directly related to the content itself. Some content is good, some content is bad.For example, sometimes this informational content has explicit publicity about sexual or illegal themes.
I believe that you should change 'or' to 'and'. Also change 'access' to 'access to'. Either that, or you could change the sentence to read '...teenagers access and surf the Internet...'. Again, I'm having a time issue with this sentence. Many times would imply that someone could go to the same website and 9 out of 10 times they would find an undesireable advertisment. You are attempting to generalize the entire internet, so I believe you should not be using time. Some pages never have such advertisements, and some pages always have such advertisements. As a result, I believe that you should use 'in many cases'.Nowadays, a considerable number of children or teenagers have access and surf the Internet, and many times this explicit publicity is easy to find on various web sites.
Therefore, it is necessary to control and censor undesirable explicit material that could be injurious to our sons.[/quote]
If you would like to avoid any sensitive gender inequality issues, you may want to consider changing 'sons' to simply 'children'. Also be careful, I believe that you mentioned that this was an introductory paragraph. Therefore is a concluding word, and you may be penalized for using such a strong word to end your introduction. I get the impression from this paragraph that you are allowed to write in first person, so maybe consider 'I believe it is necessary...'.
Basically, with all of my suggestions, your paragraph would appear as such:
As an afterthought, I changed 'injurious' to 'detrimental', a decision purely based on familiarity.In my opinion, material on internet should be censored or controlled because much of this information can go around without any kind of control. For example, sometimes internet content has explicit publicity about sexual or illegal themes. Nowadays, a considerable number of children and teenagers access and surf the Internet, and in many cases this explicit publicity is easy to find on various web sites. I believe it is necessary to control and censor undesirable explicit material that could be detrimental to our children.
I hope this was helpful.