Fire officials say three other people who were in the house have been hospitalized with what appeared to be non-life-threatening injuries.
The State Fire Marshal's Office says the fire started on a front porch where there was an incubator.
Officials identified the children who died as 12-year-old Faithlyn Bogavich, 4-year-old Delaney Bogavich and 1-year-old John Jeffrey Bogavich.
The others injured included a 13-year-old boy.
The two-story house in Jeromesville was fully engulfed in flames when firefighters arrived at the scene about 70 miles (113 kilometers) southwest of Cleveland.
At least six fire departments responded.
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