Mine are age 8, 7 and 5, GBG.
I answer questions as they come up, they don't come up very often though. They don't see any gay relationships anywhere, the only gay friends we have are habitually single, so they're no good as role models 
They need to know about the mechanics, internet, bullying/pressure, gay relationships, periods, everything really, although not all at once and not all now.
I always hope things will just come up naturally and I won't have to ask them all to come in and sit down because I have 'something to tell them'.
Advice please!