minor molested by another minor

my son happens to admit that a classmate of the same age molested him 2 or 3 yrs ago, apparently the alleged classmate performed an oral sex on him and instructed my son to do the same, at that time they are both in fifth grade. my son now is in 3rd yr high school and what happened is the alleged classmate is circulating a rumor that my son was the one who is gay and was the one who did the act. So naturally my son reacted and they got into a fight, which pushed my son to admit it to me (4 yrs late). I was devastated, i wanted to sue the other kid!, what will be my legal rights or what are my options. I cannot just shrug this off. Please help me.