Of course you can, but should you? It is a tough decision because you don't want to file charges against someone who is innocent and ruin their life, but it you don't then you may not be helping a minor. Also, filing false charges is a crime, not to mention someone may not like you filing charges against them and may retaliate.
I would wait until you have something a little more certain. Because right now you are "wondering" and "suspecting". How would a prosecutor proof a case like that anyway beyond a reasonable doubt? Give it a little time, but if you just can take the suspense anymore, then call the state attorney in your county. Please click on the website, it does not cost anything. Thank you.
You cannot file charges; you can file a police report or contact children's services about your concerns. If your suspicion is not well-founded, you will bring years of grief to many including the child you are trying to protect. But if you don't act and your hunch is correct, you'll regret not acting. You say you don't have proof or evidence, so what makes you suspect sexual misconduct? How well do you know the child and the person whom you suspect? Do other adults who are close to the child share your concern? Has the minor said anything to confirm your suspicion? Is the child old enough that s/he would likely tell someone? Have you witnessed something inappropriate? I think the right decision depends on your answer to those questions and others like it.