What is the ruling on interacting with immature girls, in terms of looking at them, speaking with them, and laughing, and is the ruling linked to their size?

If the girl is young and has not reached the age of desire, she does not take the ruling of a non-mahram woman (ajnabiyyah). It is permissible to look at her, touch her, and speak with her. Some scholars have estimated this to be at four or five years old or younger. The apparent understanding is that it is not restricted to a specific age. However, the Malikis hold that it is not permissible to touch a girl who has reached three or four years old, even if it is permissible to look at her. A girl who has reached nine years old or is close to it takes the ruling of women; therefore, it is not permissible to look at her or touch her.