Thank you for your email and very kind words about my site.
I understand you are disappointed that your son didn't come to you with his questions. It is not always easy for children to ask their parents sex related questions and therefore as parents we need to be talking about sex to our children, even if they don't ask us. Bring up topics in the car when you drive if you find sitting down with your child awkward. I will be posting an article on how to talk to your children about sex soon. Research shows that children who learn about sex from their parents are less likely to engage in high risk behaviour and are more likely to abstain from sex until they are older. So information is power.
Most children turn to their friends or older siblings to answer their questions as they fear their parents reaction, and because they are afraid their parents will think that their questions mean they are interested in having sex when in fact they just want information. I would not recommend that you prevent your son from asking questions from your brother's girlfriend, especially if he feels comfortable talking to her and you are able to discuss with her what was said. It is important though to give him accurate information so you could say something like: "I believe you spoke to .... about ejaculation and I just wanted to ensure that you have all the correct facts. It is normal for boys your age to begin having ejaculations. Sometimes they happen when you are sleeping and we call them wet dreams. This is nothing to be embarrassed about and it shows that your body is healthy and developing normally." You could then explain why it happens and the role ejaculation plays in creating a baby.
Congratulations on being open about talking about sex with your children and 10 years of age is not too young to give him the book. Although I would recommend reading through it with him and discussing the changes he is or will be experiencing .
Moving forward you need to talk to him about:
Respecting women and treating them well
Respecting the word NO
Having safe sex and sexually transmitted diseases
Sexual pleasure and self stimulation as an alternative to sex
Sex creates babies and the cost and responsibility of having a baby at a young age
Sex, the internet and cell phones
The importance of a loving relationship, and making wise choices.
It is not necessary to give him all the information at once but rather find opportunities while watching television or in everyday life to teach him about sex as well as about values and responsibility.
In a couple of years you will need to give him more specific information about oral & anal sex, pornography and sexual abuse, gay and lesbian relationships and so on. Always find out what he knows on the topic already and then ensure you give him accurate information.
Keep up the good work.