The boy, who had vision issues, leaned forward and fell into the exhibit after his mother lifted him onto a wooden rail overlooking the enclosure. He was immediately attacked by the dogs and bled to death.
The mother won't face any charges in the Nov. 4 death. Prosecutors called the boy's death a "tragic accident." The district attorney's office is still investigating whether anyone at the zoo might face criminal charges.
The wooden platform is surrounded by wooden rails about 4 feet high and, below the front railing and on the sides of the platform, clear plastic or metal mesh to prevent anyone from going into the exhibit about 10 feet below. But in front of the platform, there is nothing to prevent someone from falling into the exhibit.
The exhibit was closed indefinitely, and the dogs were being quarantined for at least 30 days. It was not yet known if the dogs would be exhibited in the same open-air enclosure again. Zoo workers are checking other exhibits to make sure they're safe.
The Associated Press contributed to this report.