This can all be answered very simply:
1) If you feel a crime occured, contact the police department.
2) Based solely on your post, it is POSSIBLE that the persons who did the assault could be liable for civil damages. To what extent depends largely on the FULL facts and whether he can prove that a person or specific persons were responsible for his injuries.
1) Were your son and his friends invited to this 'party'??
2) If not, what EXACTLY did they do when asked to leave and why didn't they leave??
And I agree, you (or we) are not hearing the full story here.
There are at least 17 lawsuits (!!) filed in various courts, including the US Supreme Court, asking if Obama is a natural born citizen (as req'd by Art II, Sec 1 of the US Constitution).
Why has he spent over $1.7M in legal fees to block disclosure... rather than spend $12 for a VALID birth cert to settle the matter? The 'certificate' he has presented doesn't qualify to get a drivers license, wouldn't allow a child to qualify for Little League, or for a real citizen to get a US passport!