I do not yet have any children (as I’m 19 years old, unmarried, and I do not believe myself to be nearly mature enough yet for such responsibility), but I do plan to have kids one day. My ethical reasoning for this is that I believe that for the vast majority of humans, we find it better on the whole to exist than to not exist, proof of that being that most of us don’t wish to commit suicide (for the most part), even in extremely trying situations. Even if the world were falling apart (which admittedly it sometimes feels like it is), most of us would still fight to stay alive, because we value our own existence, and the existence of others. As such, I see it as a strong moral positive to bring more people into existence, and having biological children is an excellent way to go about doing that.
The same, I’d think—most people would rather exist in an overpopulated world than not exist at all, so it would still be morally worth it, in my opinion. Many of my friends are the grandchildren of holocaust survivors, who had children while stuck in the objectively terrible and overcrowded post-war camps, and I am glad they did have children despite the horror surrounding them, and the uncertainty of if their children would ever escape it.