No charges had been filed Sunday, but McHenry County Sheriff Keith Nygren said it was being investigated as a crime scene.
Neighbors said the attacks started late Saturday afternoon when children going door-to-door for a fund-raiser arrived at the home of Scott Sword, 41, who owned the dogs.
"We had music playing, and I heard this bizarre sound," said Debby Rivera, who lives three houses away. "I looked out the window, and I saw a young boy. The dogs were just jumping on him."
"The screams were horrible," she said. The dogs were "relentless, like they were possessed."
The pit bulls attacked the two children, and when the dogs' owner tried to stop them, the dogs turned on him and bit off his thumb, Nygren said. The boy's father also tried to protect his son and was attacked. The dogs went after another neighbor as well.