Hello again and thank you for the information. First, I will note that although you still didn't provide any detail on what is meant by him "liking" little boys, if he is engaged in person to person contact with boys that is illegal, this should be reported to local law enforcement, not the Feds. However, if this is child pornography, then the Feds are the appropriate agency (although you can also report to local or State law enforcement), and the Feds do take this very seriously.
As for the Navy issue, he is not subject to the Uniform Code of Military Justice unless he is on active-duty orders or in an active drilling status, so "conduct unbecoming" would not be an option unless he is caught doing something illegal in that active status. He is basically a "citizen" servicemember and his criminal conduct would be handled by the civilians. That said, if he was arrested or convicted by the civilians for a crime, he could be administratively separated by the Naval Reserve for that civilian misconduct. But first, the civilians need to address any illegal criminal behavior.
So, if that occurs, then he could be reported to the Chief of Naval Reserves, or his local Reserve Command. Please feel free to ask follow up questions if you have them. If not, if you could take a moment to leave a positive rating in the box above, I will receive credit for assisting you today. Thank you.