Why does a 6-year-old boy touch the mother's penis? Is it normal?

Patient's question:

Patient Gender: Yan Zhiqiu
Age
Detailed Medical Condition and Purpose of Consultation: Why does a 6-year-old boy have penile erections when in contact with the mother? Is it normal, and how can it be prevented and treated?
Duration of Current Illness: Every night when sleeping with the mother
Current General Condition: Generally normal
Medical History: 1 year
Previous Diagnoses and Treatment History and Effects: None
Auxiliary Examinations: None
Other: None

Doctor's answer:

Hello, an erection of the penis in a 6-year-old boy is usually an instinctive response and is normal. There is no need to worry.