Last article I saw indicated that the staff were certain, as soon as they arrived on scene, that the boy was dead. Same article said the zoo CEO says evidence indicates the fall did not kill the child, the dogs did.
There is a safety net in place, in case of falls, but the boy was so light he bounced out of it and into the pen.
No punishment can match what that mother is doing to herself, and anybody can have a dumb moment... but I see a lot of parents who seem to have no concept of risk analysis.
It probably never occurred to the mother that her toddler could fall off the fence, or that dogs could be dangerous.
Then again, a parent I did not know once not only allowed, but encouraged his diaper wearing child to jump on my Rott-Shepherd, in an apparent attempt to use the kid to get my ex-wife's attention. Never occurred to the guy that the dog could eat the kid (or that the woman might have a reasonably large husband in the nearby surf).
Over the years, I have seen a lot of people allow or encourage foolish behavior by their kids with regard to animals.
The zoo incident saddens me, but it does not surprise me.