The incident happened under Dumra police station area when they had gone there to make a Chhath puja ghat, the police said.
The two slipped and fell into deep waters while preparing the ghat at the pond, Sadar Sub-Divisional Officer (SDO) Satyendra Prasad said.
The deceased were identified as Rakesh Kumar (11) and Dipali Kumari (08), the SDO said.