All three injured boys were admitted to a hospital as one of them suffered critical wounds.
The boys whilst on the way to the school found a round-shaped object and as one of them picked it up assuming it could be a ball lying near a pond, the crude bomb went off wounding all.
The mishap happened around 0800 hours on Wednesday.
The trio were admitted to the Jangipur Mahakuma hospital.
Meanwhile, police also unearthed a drum full of crude bombs, concealed in a bush at Harihar Para village, also in Murshidabad.
Police called the bomb defusing squad to deactivate the explosives.
(With UNI inputs)