Work was being done on the duplex's water line when the gas line was struck, causing the explosion Saturday, Fairborn Fire Marshal Carl Day said.
A 13-year-old was transferred in critical condition to Shriner's Hospital for Children, one of about four hospitals in the country specializing in pediatric burns, said spokeswoman Louise Holker. Two men also were injured. Their conditions were not given.
The 1-year-old baby was in fair condition and a 5-year-old was in good condition Sunday morning, a spokesman for Dayton Children's Medical Center said. A third child, whose age wasn't available, was treated and released Saturday.
The blast was one of three in the Midwest over the weekend. Another in Benton Township in southwestern Michigan killed two people late Saturday and injured four others. Its cause wasn't immediately known, but relatives say several oxygen tanks were inside. And an explosion in Chicago on Sunday morning flattened one home, scorched others and sent two people to the hospital with serious burns. Fire officials and utilities were investigating.
A woman who lived about 100 yards from the Ohio home that exploded, Cybil Poole, told the Dayton Daily News that the blast felt like a car hitting it. She said she saw the infant lying in the yard and that some of the other victims were still on fire.
"It was horrible. It was like a movie scene. You see this huge fireball and you see people come out of it on fire," she said.
Another neighbor, Paula Corelli, told the newspaper that she was almost hit by a flying piece of wood from the explosion. When she saw two adults running down the sidewalk carrying three bloodied children, she offered to take them while the adults returned to the scene.
"Medics told me to keep them awake because they had head injuries, so we sang to them, me and another woman," Corelli said. "And we didn't let them look back. It was still on fire and there was a lot of blood."
Some of the victims were airlifted to hospitals.
Windows shattered on homes on both sides of the destroyed house. Debris could be seen a block away, the Dayton Daily News reported. The gas was turned off to the house that exploded, Day said.
Several others in the neighborhood were evacuated as a precaution, but some residents were allowed to return hours later.
Chase Kelley, a spokeswoman for Vectren Corp., said it hasn't been confirmed that there was a gas leak and the company would likely conduct its own investigation into the cause of the explosion.