The incident occurred in Ramkantapur village on Friday, said Singair Police Station OC Khondker Imam Hossain.
Police described it as the outcome of an acrimonious relationship between Rina Akhter, 28, and her husband Abdul Aziz. The in-laws tortured Rina mentally, the police said.
Their children Afrin Akhtar, 6, and Abdul Momin, 4, have been admitted to Dhaka’s Shaheed Suhrawardy Medical College Hospital.
“On Friday evening Rina poisoned the children and took poison herself. They were taken to local hospital for treatment, where doctors declared Rina dead and administered first aid to the two children.”