Years ago, I remember watching someone playing with this mod, and showing his child, whose skin was a mix between the player´s and his wife´s skins. However, in the version I´m playing - 5.3.1, for 1.12.x - I´ve tried having children to see if this could happen, but every child just has a random skin that doesn´t fit when you look at the parents. It is odd that two villagers of color can have a white child. Besides, I love genetics in videogames, and I´d love to see my children inhereting things from my spouse and I.

I don´t know if this would be to hard, or even impossible, to do, but I´d personally love it. Still, I´m learning how to make skins and I know how to place them inside the game, so, until then, I can always make my children´s appearences. Thanks for reading!

This would be near impossible without any machine learning algorithms to generate skins for you.
Can you link the video you watched? Perhaps the video creators did some things behind the scene such as edit the baby skin to make it look like there were genetics.

Al through still quite some work, you can define 2-3 different genes (color, ...) resulting in samples^3 different textures, then interpolate and slightly randomize the result. Therefore, it's possible to implement, but requires more interest first.