The incident took place on the outskirts of Ramapuram village of Vetapalem mandal. The children had gone for a swim, said Chirala rural inspector Mohd Feroze.
The deceased were identified as V Sujata (7), Anjamma (10), V Ramudu (8) and their cousin Nagaraju (9).
Their grandmother Nagamma (50) died of shock after learning about the children's deaths.