The police have booked three persons under the Pocso Act in Chennai and Kancheepuram districts.
Murali, 36, of Tirunindravur was arrested for sexually assaulting his 16-year-old daughter and the 13-year-old daughter of a woman with whom he was in a relationship.
Murali is a history-sheeter, and along with his daughter he stays in the house of his partner.
Over the past few months, he had been sexually assaulting the two minors.
Recently, the two girls informed the woman about the crime. She lodged a complaint with the Avadi all-women police station.
Murali was arrested under the Pocso Act, and has been remanded in judicial custody.
In another case, the Ayanavaram police arrested Venkatesh, 21, for kidnapping and sexually assaulting a minor girl.
The police said Venkatesh, from Tirutanni, kidnapped the girl and sexually assaulted her.
She managed to reach the Tiruttani railway station and was rescued by the railway police.
She was handed over to Ayanavaram police station personnel as her grandmother had lodged a complaint. Venkatesh was arrested from Andhra Pradesh.
Gunasekaran, 60, was arrested under the Pocso Act for sexually assaulting his 12-year-old neighbour. Her parents came to know about the crime after she became pregnant.
A complaint was lodged with the Uthiramerur police station and he was arrested.