well legally the situation falls under "lethal force to prevent injury death to bystanders". so legally nothing could be done to you. and yes the zoo could sue you for "property damage" but only an activist judge would have convicted you of it, seriously no judge that wants re election is going to punish the person who shot some zoo animal to save a little kid.
the whole source of the tragedy doe not lay with the zoo.
the employees didnt want to go running in, saying they thought the child was already dead is useless, its a human, they have to assume the person is alive. people who get hit by semis are still considered to be alive until the ambulance gets there to make that determination.
but ultimately it comes to the mother who obviously did not read the safety warning signs on the fences.