There are several reasons why children can't enter the ancestral graves after death:
1. Traditional concept: In the traditional concept, only adults can become members of the family and be included in the ancestral graves. Children are regarded as the future of the family, and their death is regarded as an unfinished life, so they can't enter the ancestral grave.
2. Age limit: In some places, it is clearly stipulated that only people who are 18 years old or married can enter the ancestral graves. This is because they believe that only adults or married people can be accepted by their grandparents if they have the ability to take on family responsibilities.
3. Religious belief: In some places, people believe in Buddhism or Taoism. They believe that the soul will enter reincarnation after death, and the child's soul is not mature enough to enter the ancestral grave.
4. Geomantic considerations: In some places, people think that the location and layout of ancestral graves will affect the family fortune, so they will choose to bury their children in other places so as not to affect the family fortune.
Generally speaking, children can't go to ancestral graves after death, which is mainly influenced by traditional concepts, age restrictions, religious beliefs and geomantic considerations. Although these regulations and customs may no longer be strictly observed in modern society, they still affect people's behavior and thoughts to some extent.