Parents ought to be the first source of sex education for their children. Don't think that because children can learn about human sexuality in school, your responsibility to teach them about sex has been removed. Especially now that there is confusion as to how to teach human sexuality in school, the parents must be ready to assume the role to educate their children in everything they need to know to understand their sexuality.
Who's better to teach about morality and the ramification of sex and sexuality to your children than you their parents? Often times, the school only teaches about the anatomy of human sexuality and the issue of morality and the taboos related to sex are often placed on the sidelines. This is where you should come in - teach your children their moral obligation when it comes to sex.
Sex education does not involve only teaching the children about the anatomy of the human reproductive organ. It's much more than that. Sex education also involves teaching the children their moral obligation towards the opposite sex. Even more so for teenagers, you need to teach them their moral obligation towards their boyfriends or their girlfriends for that matter.
More so if your teenagers are already sexually active. You have an obligation to open their eyes about the possible ramification of their action. Your son could get a girl pregnant or your daughter can become pregnant if they are practicing sex at a very young age. They should understand the implications of their actions.
Another very important aspect of sex education you should teach your children is the issue on sexually transmitted diseases. If they are already sexually active, they must understand that they can contract disease by sleeping around with many partners, or even from their very first sexual encounter
Sex education is always a difficult topic to discuss with your children at home. But this is yet another role of parents that they cannot escape from.