They said the one-and-half-year-old daughter of army jawan Manjeet Singh, who had received bullet injuries in her head and leg, could not be saved despite a surgery.
Manjeet Singh and his five-year-old son had also died in the suicide attack by militants.
Meanwhile, the condition of four of the 47 injured continued to be critical, the sources said.
Thirty-three persons were killed when heavily armed militants attacked passengers of a Jammu-bound bus at Kalu Chak and stormed the nearby army camp, on the outskirts of Jammu city on Tuesday morning.
In retaliatory action, army commandos gunned down all the three members of the suicide squad, which had carried out the attacks.
Defence Minister George Fernandes and Union Minister of State for Home I D Swami visited the army hospital on Wednesday and inquired about the condition of the injured.
Congress chief Sonia Gandhi is also scheduled to visit the hospital, the sources said.
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