The deceased have been identified as five-year-old Prem BK and three-year-old Basanti BK. They are son and daughter of Ganesh BK of Tribeni rural municipality-2.
According to the District Police Office, Rolpa, Khadka Bahadur BK, 21, of the same village had murdered the minors by attacking with an axe.
Deputy Superintendent of Police, Gyanendra Phyunal, said that police have arrested Khadga Bahadur on Monday night itself.
Accused Khadga Bahadur is uncle of the deceased, it is learnt.