The district's Additional Superintendent of Police Liton Kumar Saha said the two were caught in a clash around 10am Tuesday at Borokanda village in the Upazila's remote Haor area, Dhaki Union.
At least 25 others injured in the armed clash.
The deceased have been named as 9-year old China Akter, daughter of Moksed Ali, and ‘Mozakkir’, 12, son of Mohammed Ali, of the village.
Police quoting residents said there was a long-running feud between the Awami League's Borokanda ward unit President Haider Ali and Dhaki Union Parishad member Basir Miah.
Following overnight altercations, the two groups armed with local weapons clashed in the morning.
Stabbed with spears, both died on the spot, ASP Saha said.
He added that additional police were deployed in the area and the situation was calm at the moment.
The injured have been hospitalised at Mithamoin and Kishoreganj.