The incident came to light after the kindergarten student, who went to the accused's house on March 23, complained of physical discomfort later and was hospitalised.
Based on her statement and a medical check-up, the Child Welfare Committee filed a case against the neighbour, and a probe was initiated.
Meanwhile, the child's relatives have allegedly accused the police of laxity and inaction, claiming the accused wasn't arrested earlier despite the complaint being filed days ago.
The incident throws light on yet another case of child sexual abuse, which has been on the rise in Kerala.