Authorities are investigating whether owners, employees or government officials could face negligence charges after a fire raged through the ABC day-care in the northern city of Hermosillo on Friday, Attorney-General Eduardo Medina Mora said.
"The fire was caused by the overheating of an air conditioner due to continuous and prolonged use," Medina Mora told reporters.
After melted aluminum from the air conditioner ignited paper on the floor of the warehouse, where the state government stored license plates and documents, heat and fire spread into the rafters of the industrial building and across to the day-care center, he said.
He said nobody was in the warehouse when the fire started and that its doors were locked.
As the smoke poured from the day-care center, bystanders and firemen punched holes through its brick walls to reach the infants and toddlers. Questions have been raised about whether evacuation routes in the building may have been blocked.
More than 140 children were in the center when the fire broke out, the government says. The facility had passed its last government inspection in May.
Some severely burned children have been flown to specialist hospitals, including the Shriners children's hospital in Sacramento, California.
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