How can one deal with a nine-and-a-half-year-old male cousin who kisses and hugs a three-year-old girl, and how can he be convinced to stop, especially with his mother encouraging him on the pretext that he is male and has not yet reached puberty?

Based on the hadith: "All of you are shepherds and all of you are responsible for your flock," protecting children from sexual abuse is the parents' responsibility. What happened to your daughter is considered sexual abuse, whether intentional or not. Sexual abuse is exposing a child to any sexual content or behavior. Sexual abuse is divided into unintentional (such as intercourse in the presence of the child after they turn one year old, or nudity in front of them), and intentional, which includes harassment (such as peeping, touching the child's private parts, direct sexual speech, and showing pornography), and rape. The immediate imperative is to sever all forms of communication between your daughter and this boy, regardless of his mother's reaction, primarily for the protection of your daughter.