I didn't do an exhaustive search, but this is what I remembered from my days in the KHall.
Though not all sex abuse is by a blood relative, the fact that incest, etc. was covered in Leviticus Chapter 18... close enough for me!
Leviticus 18:6: "You people must not come near, any man of you, to any close fleshly relative of his to lay bare nakedness. I am Jehovah." (Even though it says, "any man of you," the principle would apply to those who may not have reached full manhood yet, I would think).
Sibling "Sex Abuse": Lev. 18:9: "As for the nakedness of your sister, the daughter of your father or the daughter of your mother, whether born in the same household or born outside it, you must not lay bare their nakedness."
"Sex Abuse" by a Grandfather: Lev. 18:10: "As for the nakedness of the daughter of your son or the daughter of your daughter, you must not lay bare their nakedness, because they are your nakedness."
Step-Family/Sibling "Sex Abuse": Lev. 18:11: "As for the nakedness of the daughter of your father's wife, the offspring of your father, she being your sister, you must not lay bare her nakedness."
(vs. 12-13-14-15-16 deals with aunts, uncles, daughters-in-law, sisters-in-law).
"Sex Abuse" w/mothers & daughters & granddaughters: Lev. 18:17: "The nakedness of a woman and her daughter you must not lay bare. The daughter of her son [granddaughter] and the daughter of her daughter [granddaughter] you must not take in order to lay her nakedness bare. They are cases of blood relationship. It is loose conduct."
There may be other scriptures that apply in principle (i.e., not to lay down with father's wife -- in reverse that would be "sex abuse" of the wife with the son; and the scriptures of men lying with men -- at whatever age, in principle, would be the same as "sex abuse" of boys).
"Do not make yourselves unclean by any of these things, because by all these things the nations whom I am sending out from before you have made themselves unclean. Consequently the land is unclean, and I shall bring punishment for its error upon it, and the land will vomit its inhabitants out. And you yourselves must keep my statutes and my judicial decisions, and you must not do any of all these detestable things, whether a native or an alien resident who is residing as an alient in your midst. For all these detestable things the men of the land who were before you have done, so that the land is unclean.... In case anyone DOES any of all these detestable things, then the souls doing them must be cut off from among their people. And you must keep your obligation to me not to carry on any of the detestable customs that have been carried on before you, that you may not make yourselves unclean by them. I am Jehovah your God." (Lev. 18:24-30)
I agree with Plum - COMMON SENSE.