About women? I think I should tell them that Allah has made the females for males and vice versa. In this day and age especially in the west where they started teaching about gay rights, I think I should start filling my boys ears on how wonderful the women are and the male should only have sex with females.
My boys are 9 and 8.
In all seriousness, you do raise an excellent point.
They're a bit young yet. For now tell them that thier genetalia is a private part of their body and that nobody else should be allowed to touch them there, or ask them to touch any genitalia. Tell them that if anyone touches them there or asks them to touch those parts - to run away and to tell you as soon as possible, whoever it is. It's important that your boys don't fear you, rather that they trust you and know they can confide in you - even when they've done wrong.
Another important thing to do is make sure you know where your boys are, they should never be in a private place with another adult, even if it is your own family.
In 2-3 years time they will be starting puberty, at that point you need to tell them about the hygiene aspect and about purdah, how it applies to men. At that point you can explain to them that their bodies are changing from those of boys into men and explain how the physical change will happen such as growth, body hair, change in voice, appetite etc.
Wait until they are 13-14 to tell them about sex. Just explain the biology of it, what an erection is, what purpose sex serves (breeding), how it's a normal human desire, how men and women are partners for each other. You are also responsible for telling them about their religious obligations, the social impacts of haram relationships and why it's important to avoid **** and masturbation wherever possible.
We've all been teenage boys, we've all done it, but it's important to help them understand the negative impacts early. it skews their perception of physical relationships, it desensitises them (in extreme cases physically), it can be addictive.
When the time is appropriate you have to be well researched, honest, open and candid.