When the child reached his home, he was crying and told his parents about the incident, police said.
The victim's parents informed the police and also took their child to hospital as he was bleeding, police said, adding that Rajesh was arrested the next day.
The court also rejected Rajesh's plea that he was falsely implicated in the case by the child's parents as they had a quarrel with him some days ago.
"The child, when examined in the court, very confidently and without any hesitation firmly stated that the accused had committed wrong act with him," it said.
The court will decide quantum of punishment next week.