One of the most interesting aspects of having multiple children shared with a single spouse is how it brings the hammer of reality down on your thinking. The sort of thinking I'm discussing here is thinking on how all of your children are the same and how they are different. When you only have one child, it's easy to pretend that things might be a fluke. It's also easy to pretend nonsense like a child's gender being 'socially constructed' and not real at a gut level.
Looking at my two little ones would beat that out of me if I ever truly held it. For instance, give the little boy a toy sword, and what does he do with it? Why, he flourishes it with an excellent grip and proceeds to whack at the floating balloons nearby, or anything else identified by his parents as a legitimate target (he's been taught that he's not allowed to swing at anyone who isn't holding a similar weapon themselves). Give the little girl a sword, and she too will flourish it with a remarkably effective grip for a one year old. The difference is she uses it to get attention and to flirt with, flashing a huge grin and capturing the eyes of passers by, such as women of grandmotherly age. She won't try to whack at anything with it, despite never having been discouraged from so doing. One displays typical little boy behavior, and the other stereotypical little girl behavior, with no particular prodding required at all.
Another big thing one learns is that despite possessing very similar genetics and an extremely similar environment, each child really is significantly different. All we can do in essence is determine what tables their attributes will be generated using, it is not to us to determine the exact fall of the dice.