I just realized that most of the cast is in their lower to mid 20s if they even are in their 20's... They act like they are my age or older.... Zack is as old as me and feels like a 30 an immature 30 yr old.
It's seems implausible that anyone went to college. I bring this up because Lisa is supposed to be a scientist. I would put it past her that she is no less than a prodigy, but it seems silly for her to be in the employ of Donovan at 20 yrs old or younger with as much intelligence as she has and was able to learn how to fight AND be some sort of wrestler on the low.
All that to say, due to her age, it would make Leon 22ish when he would have impregnated Lauren, who then later died. Any theory on how Mila came out of that is spurious. While the age might be right for a young Leon, any Bayman hit on him doesn't make sense based on the wikia. Bayman would be around the same age and both apparently know each other as deserters while having a positive relationship. If anything happened that would harm the life of a potentially known unborn child, I don't think Leon would be the man to not harbor negative feelings towards Bayman. Furthermore, based on the wikia, Leon was with Lauren when she died in a desert. She would have had to be in her latter terms of pregnancy for it not to be noticed by Leon who would try to save the child should she have died in labor.I highly doubt Leon would have gotten her pregnant, left her whilst in love with her, comes back when she had the child and without any postpartu effects, and they resume their love dream until her demise. It would have to be the case that she gave the child away long before Leon's knowledge, but I don't think the time frame allows nor the limited lore allows for Leon to have not known or had left her in the meantime..
Yet the etymology of her name is "Miracles" and I believe Mila was raised by rich folk. Money fills in the blanks in any sort of plothole. Mila was abopted by some rich folk and raised elsewhere. It can work, especially if her unknown causes of death was due to having Mila. If she was a battlefield baby, I'm sure Leon was smart enough to know that he couldn't provide for her. But, he would be torn giving away the only thing in the world that reminded him of his love.