You're at the zoo. Read the signs - you know, situational awareness. Apply some simple logic and look at the type of barricade using to keep you safe. Note that the animal is a pack hunting carnivore. It isn't rocket science and when you see the dogs mauling the child, you gotta understand, even at the most basic level, that these are not bunny rabbits licking melted snowcone off the child.
Not kept hungry? Not hunting because they need to hunt? I am fairly certain you have misunderstood the situation. No, the dogs would not be kept starving, but unlike your pet poodle, they aren't going to have a dish out where they have African Painted Dog chow out for on-demand eating. Like the other carnivores, they are likely fed on a schedule that matches their schedule in nature as is most reasonably possible by the zoo. The dogs probably hunt, attack, and kill once a day or when hungry. So unless the dogs have just recently eaten, they may be VERY HUNGRY. For all you know, it is just before feeding time when the animals are their most dangerous. The child falling in may be just like when the zookeepers toss in large carcass chunks.
To make such naive assumptions that the animals are somehow specifically timidly around adult humans would be one of those gross underestimations of one's opposition, especially when dealing with packs.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011