After a slight decrease from severe levels, the mercury is hovering around 40 degrees Celsius in most regions
The deceased are cousins - Asma Akter, 21, Sadia Akhter, 14, and Shakibul Hasan, 10. Three others are injured in the accident.
Pagla Police Station OC Chan Mia said the boat capsized in Boladair canal in Islampur village around 6:45pm on Sunday.
Tajul Islam, a member of the local union council, said the six were crossing the canal on their way home after visiting a relative's house as part of Eid celebration.
The three survivors were given first aid, he said.
OC Chan Mia said the bodies were handed over to the families without post-mortem examination on their request.