You can directly call your best friend's child's name, or call him by his nickname. When she calls you daughter, you can also call her by her first name or nickname. As for the children of both parties who are very young and not related by blood, just call them aunt.
Concept:
A woman will always have one or a few close friends in her life. Even if she has experienced great success and has descendants, it will not prevent them from making good friends. Best friends, the reason why they are called secrets must be related to secrets. Many issues that are difficult to talk about and are too shy to discuss with the opposite sex can be discussed with best friends.
When women want to confide or discuss private issues, they will most likely choose a close friend. Therefore, best friends generally maintain relationships for a long time, and it is generally difficult for two people to break up the relationship.
Girlfriends usually talk about private female topics such as love, emotions, sex, and physiology. Therefore, bestie is generally an exclusive pronoun for girls, and with the development of society, more and more girls are using this pronoun for boys.
A male best friend, also known as a "blue-faced confidant", refers to a close male friend who is close to a woman and talks about everything.