The injured are mother Rahela Khatun, 48, her daughter Ripa Khatun, 26, and minor son Yeanur, 8, of Gadkhali village under the upazila.
Quoting locals, officer-in-charge of Jhikargacha Police Station Nur Mohammad Gazi said the accused Jasim, 35, a day-labour who works at a neighbouring house had offered to marry Ripa several times, but was refused by the woman.
Enraged by it, Jasim earlier allegedly threatened Ripa to take revenge and around 8:15pm on Thursday he threw acid targeting them through windows, leaving them injured, he said.
Hearing screams, neighbours rushed to the spot and took them to Jashore General Hospital where they are receiving treatment, the OC said.
The boy was hurt more than his mother and sister, he said, adding that police are trying to detain the accused. Police are dealing with the case with importance, reports UNB.