Growing up i never really had anything like this explained to me by my parents, i just figured it out along the way. I still remember when i found out what 'gay' was. My cousins were laughing at me because i didn't know what it was and i said... 'doesn't it mean you are happy??' I can't remember how old i was but i would say older than 10. Even though it was never fully explained to me it was never looked down upon either. Just not discussed.
Reading your post has made me realise that it is important to discuss this with my children in a relaxed manner so when my children do come across a friend who is gay, has same sex paresnts (all of the varying relationships there are) he will understand straight away and it will not be such an unknown as it was for me.
I am one of the ones who has not thought of discussing it with my child yet but they are still too young. I thank you for bringing such a thing to my attention and i will do my best to make a point of ensuring my children are aware of all the diverstiy in the world and to accept each and every person the way they are.

