It takes years for kids who experience some or the other sort of child abuse to come out and speak about it. Some do not open about it until they turn 40. Most of the times they think it is their fault. You can check the statistics yourself of the number of boys and girls sexually abused. Sexual abuse isn't always about raping, as per Wikipedia definition of rapes. Sexual abuse is also about being inappropriately touched which is usually shrugged off as "just a touch". A kid mostly feels powerless and is unable to demur the act. Teaching a kid to say no isn't enough. Instead make that comfortable place for your kid so that he/she can come and tell you about it all.