It is funny how it's a different world for things like that now. My kids are growing up in a world which maybe still isn't perfect, but in which these ideas are mostly handled in a very matter-of-fact and positive way, both on and off screen. And I'm sure seeing gay relationships depicted on-screen reinforces their understanding of the gay couples they know in real life.
I know shows like Doctor Who have been criticised in the past for going too far in actively promoting gay and bisexual relationships, but I disagree - as this conversation demonstrates, it's often through TV shows that we learn about the world around us, when we're young, so I think it's the perfect place to address those ideas clearly and openly.
I'm sure (or at least, I hope) that when they grow up my kids are going to be just as horrified/mystified about how things were when we were young as we are about the kind of inequalities from the era of our own parents.