Numerology Feng Shui: What is the eldest son and eldest daughter?

For a simple example, we have a saying that strangle in the cradle. Since I have never been in this world, why are there long words? The first born is counted as the eldest son or eldest daughter. But in numerology, it is possible that people will predict that you have an abortion or something. But generally speaking, the eldest son and the eldest daughter are born. This question is simple.