Are most sex offenders heterosexual?
Yes. Most sex offenders consider themselves heterosexual . Jerry Sandusky and Jared Fogel are two famous examples of married, heterosexual sex offenders who fathered children.
Most sex offenders are male. Researchers agree that sexual abuse by women is under-reported and under-documented, but even with this factored in, men are more likely to sexually abuse a child then women are. 
The demographics of sex offenders mirror the demographics of America. That means no racial group, educational level or income bracket is more or less likely to be a sex offender than any other. And sex offenders are as likely to be married or married and divorced as other American men. 
People who sexually abuse children often start before the age of 18  and often don’t stop until they are too unhealthy for sexual activity. Fewer than 5% have psychotic mental illness, meaning a mental illness so severe they have lost contact with reality and may be eligible for insanity defense.
Most people who sexually abuse children also experience heterosexual attraction to adults. Someone who has sexual relationships with adult women may sexually abuse boys, and someone who sexually abuses children of one sex is likely to abuse children of the other sex. 
Sex offenders are often very likeable people who are good at getting adults and children to trust them. Sometimes they do it by pursuing careers where they help children (ie teacher or youth sports), and sometimes they do it simply by being “nice” and reaching out to children and their parents, especially children or parents who truly need some extra help.
How can we protect children?
If we can’t figure out who is a sex offender and who isn’t, how can we protect children? The only effective way is for parents to assume everyone their children come in contact with is a potential sex offender. All parents should take a class about child sexual abuse and its prevention. All parents should insist that everyone who provides services to their child (schools, after-school centers, medical providers, etc.) understand and uphold child sexual abuse prevention best practices. Parents must do everything in their power to keep their children from being in one-child, one adult situations. They must learn to communicate about sexual anatomy, sexuality and sexual abuse with children from an early age. Understanding that the world is full of people who want to sexually abuse children is terrifying, and learning that these people seem completely normal and cannot be picked out of a crowd is even scarier. But accepting the truth means we can protect children, and that’s always worth doing.