I am specifically not writing about trans* or intersex children because I am not trans* nor intersex. As a bisexual, my advice will fit (mostly) lesbian and gay children of straight parents.
Also, this is not advice for parents who are already awesome and love their non-straight children and their non-straight children’s partners. This is not advice for parents who are homophobes either – unless you want to get over yourself.
I am going to use the term “queer” to refer to bisexual, lesbian and gay unless I specifically need to refer to the individual orientations.
So your child isn’t straight, they’ve come out to you as something other than straight, or perhaps you’ve come across that knowledge some other way, and have indicated that although you’re not particularly comfortable with the idea, you still love your child – this is step one in being a good parent.
The next step might be tricky, it might be tricky because you’re from a generation that doesn’t talk much about relationships, or because you mistakenly confuse queer relationships as sex sex sex, and therefore view talking about queer relationships as talking about sex and you’re from a generation that doesn’t talk about sex.
Talk to your child and their partner about things. Talk to them both, don’t ignore the same-sex partner because you don’t know what to say or how to say it. Relationships between straight people and relationships between queer people are more or less similar. The differences aren’t so important that they need to be focussed on, and the similarities are where you bond. If your child is in a relationship with someone of the same gender as themselves, then the conversations about how they met, what they do for a living (if they’re working), their hopes and dreams and the like are just like the conversations you’d have with your child’s straight partner. It might seem awkward to you, but that’s ok – feel that awkwardness and own it. Your child and their partner live that awkwardness as society still mainly considers non heterosexual relationships to be odd, different and sometimes wrong. Your brief experience of awkwardness while interacting with your queer child and their partner, should be an empathy building exercise for you, you can begin to understand what it is like when your child and their partner exist in the wider world.
One of the most important things you can do when interacting with your child and their partner, is to not see affection between them as wrong or disgusting. You might indeed find it discomforting, but sit with that, feel it, and then remember empathy. If you see affection between opposite sex couples as sweet/cute/adorable/lovely/normal, then remember than the affection between your child and their partner is exactly the same. You’ve been conditioned to think otherwise, but don’t for the love of any deity you hold holy, say or do anything that suggests that your comfort and feelings are more important than your child’s. The more exposure you have to non-straight people, the easier this gets, and the more normal it seems (because it is).
As a straight, not entirely comfortable with queer people, parent – it is your duty as a good parent to love ALL of your child, and to work as hard getting to know their same-sex partners as you would if they brought home an opposite sex partner. It is your job to come to terms with your own internalised homo/bi/trans-phobia and and banish that from you. It is your job to educate yourself on the struggles faced by your child. There are so many people who will happily talk to you about your discomfort, your lack of knowledge regarding the LGBTIQ communities, and who can hold your hand through your own journey to full acceptance – don’t expect your child to do all the work. As a good parent, show good faith and do most of the work yourself, do not expect your child to carry the burden of your struggle to understand and accept.