1) Your marriage is solid
2) Your financial situation is solid (not just for you, but for the future human you plan on creating)
3) you at least somewhat like your job
In my expereince, if you're missing one of these three, you're in for a rough time - divorce will be a real possibility and your kids will end up hating you, you'll have to move into a 1bd close to the ghetto and date single moms, figuring out what the hell happened to your life.
just my 2 cents. alternatively, just don't have kids.