Stratified reproduction is like when you go to a birthday party and there is a fancy cake with a big piece for the grown-ups and a small piece for the kids. It means that some people get more and better things than others just because of who they are.
In the world, some people are seen as more important and valuable than others just because of things like their race or class. This means that they get more chances to have babies and their babies are more likely to grow up healthy and have good lives. Other people are treated like they are not as important and might not get to have babies or their babies might not have as good a chance at happiness.
This way of treating people is not fair and can make it harder for everyone to have a good life. It is important to remember that everyone is important and deserves to have chances to have happy lives, no matter who they are or where they come from.