1. In the past, people were poor and could not afford better things to celebrate their birthdays. Eggs are nutritious and cheap food, and have many good meanings. They are round when they are rolled up. The peeled eggs are white, smooth and clean, and the yolk is round. Eating one for a child's birthday means that this year is as flawless as an egg, and the most important thing is that this year is as "skinny" as an egg.

2. There is also an allusion: it comes from the "mysterious bird born of fate" in the Book of Songs. It is about a woman named Judy who met a swallow egg when she went out to play, got pregnant after swallowing it, and gave birth to "Qi".

Later, "Qi" became the ancestor of Yin Shang. Qi is an excellent person. Therefore, people in later generations hope that their children are as good as him, so they send swallow eggs to those who give birth to children to express their blessings, but swallow eggs are hard to find, so they are replaced by eggs.