We're about the same age I think, and I think about this too. I'm hoping that I can work out some way where they know that being trans is normal, and that I'm just as much of their father as any other kid's are even though I didn't biologically create them. I wouldn't like to hide it because having things hidden from me really, really hurt. I was screwed up for months after finding out that my parents had planned when they wanted their child and I accidently came along a couple of years before then while my mother was on birth control. It's not the same as being trans, and I wasn't in a good place at that time at all, but if something as common as an accidental birth can mess someone up then I'd hate to know what it's like finding out that your father isn't biologically your father and that he was FAAB. I'd want my child to be open minded about all things like this anyway, so while I'm planning on being stealth in the future and leading a normal male life I'd want my kid to understand that part of my life as well.
I don't know how I would actually go about it, I'd not want them to be outing me all the time at their school by saying that their "Daddy's a girl" or something, but by that point I seriously hope that I'm completely passing so no one would believe them anyway. I wouldn't want there to have to be a big sit-down talk though because our families never done that, and both me and my girlfriend (assuming that we're both still together by that point) want a family that's completely open and relaxed about everything. I think it would just be something that we didn't hide and let them know things more and more as they grew up so it wasn't a huge shock to them, and they knew that it was okay to come and talk to us about things rather than turning to the internet, although I know that they'll probably do that anyway when they reach their teens.
Some people probably want to go deep into stealth and not tell them until they're sure that they won't mention anything, but that really goes against my ethics for a family and the childhood I wished I had. Obviously you have to keep something from your children until they're older, they don't need to know details about surgeries or anything, but I can't see any reason why it would hurt them to grow up with that knowledge. And you never know when they might decide to run off with a packer, or ask the awkward question of "Why does daddy's willy come off?"
Anyway, who knows what society will be like then. One of my English teachers recently passed away in her late fifties, a year after she'd had a son with her partner, the other English teacher at my school. That got me thinking about how much society has progressed lately for gay rights -- they were both women -- and how having a child with her wife, a house together and a job where everyone knew and no one cared would only be a distant dream. It's a bit off topic, but I wondered what she'd been thinking at our age on the topic of children and what to tell them when they asked why they didn't have a father, and how much what she thought then varied to what her wife's going to tell him. With society moving how it is our plans now could soon become redundant, so I'd not stress about it too much.
