The attack happened on Wednesday morning after the boy entered the zoo by jumping over the security fence and evading sensor alarms.
Over the next half hour, he bludgeoned some of the animals to death with stones and hurled others over the two fences surrounding the crocodile enclosure.
At one point, he tried scaling the outer enclosure himself to get to “Terry”, the 11ft (3.3m) saltwater crocodile.
A turtle, four Western blue-tongued lizards, two bearded dragons, two thorny devil lizards and the zoo’s 20-year-old goanna were among those killed.
Zoo director Rex Neindorf said many of the animals were rare or mature and would be difficult to replace.