Sex of children doesn't really matter nowadays for a lot of parents, but if we are going to look back at the historical records and past events especially in a royal and patriarchal societies, it is the opposite. They wanted 'sons' because in the past, boys holds powers and legacies. In simple words, boys are more valuable, more dreamed of to have, more to say were a priority. If we are going to relate it to different movies or series that depicts this actual picture, I believe Game of Thrones is the best example or so I thought. This is where we can see that there are some deep obsession for having male heirs, pressure on women to produce sons, and the idea that daughters were just a bargaining tool for alliances and deepening power and influence.
But as the time goes by slowly, this belief are also changing. People are becoming more openminded. And I think that it's better for us to talk about old beliefs to better understand where those mindset came from, why they existed, and why are those beliefs are slowly changing to the point that they no longer serve us.
Personally, children regardless of their sex or gender or identity whatsoever deserves to be seen as enough. Not because we have to but because they are also human beings with differences.