The child, Yuridia Sosa, underwent surgery Sunday at Methodist Hospital in Indianapolis, said Lawrence police detective Gary Woodruff.
The child's mother, Mariela Rodriguez, and another woman was shot in the legs but expected to recover. The other woman's name wasn't released.
Three brothers - who witnesses said weren't invited to the wedding - got into a scuffle with guests Saturday night at a reception hall in Lawrence, a community within Indianapolis. At least two shots were fired as about 100 panicked wedding guests fled the building and ran into the surrounding park, Woodruff said.
"People were running just every direction," Woodruff said. "It was just chaos."
Officers said they saw Francisco Ponce, 21, of Indianapolis, run across a parking lot and toss a gun under a car. He was arrested on a preliminary charge of attempted murder, Woodruff said.
Ponce was being held without bond Sunday at Marion County jail, according to court records. It wasn't clear whether he had an attorney.
Witnesses said the men appeared to be looking for a fight.
"And at one point they stood up, turned a table over and started a scuffle with some of the other reception attendees," Woodruff said. "And then Francisco introduces a handgun into the fight."
His brother Isaias Ponce, 28, was charged with public intoxication, and a third brother, Jose Ponce, 23, was arrested on preliminary charges of battery, disorderly conduct and public intoxication.
Both men, who also are from Indianapolis, were being held at the arresting processing center in Indianapolis on Sunday, according court records. It wasn't clear whether either man had a lawyer.