What does it mean to be born with a blue child?

The blue here means scholar. Students in ancient times all wore blue clothes, similar to our school uniforms now. In other words, children born with reading materials will learn well in the future.

There is another meaning of being an official. Don Bai Juyi's Pipa Story: "Who cries the most? ? This Jiujiang official. My blue sleeves are wet! " The blue here is the official uniform of Jiangzhou Sima.

So I think the explanation of this whole sentence should be: children born study well and will succeed in the future.