Useful resources are the ‘Puberty’ series - Girls and Boys in Puberty. A good approach is to have boys learn about what also happens for girls (and vice versa). The Relationships, Sex and Other Stuff booklet is for teenagers (13 years or older).
The comprehensive publication Talk Soon. Talk Often. A Guide for Parents Talking to their Kids About Sex aims to increase the confidence of parents when talking to their children about relationship and sexuality topics.
Sexual Health Quarters also have many resources available for free or low cost.
For further advice on how children can best look after themselves in terms of sexual predators contact Protective Behaviours WA. This agency has a parent's handbook available for purchase.