What does Rex take his children to the zoo to do?

Rex took his family to the zoo in order to prove a point.

"I'm going to show you," he said, that no animal, no matter how big or wild, is dangerous as long as you know what you're doing."

Rex takes the kids to the zoo to prove a point about how animals aren't bad. He brings the kids inside the cheetah cage when he manages to calm him down. Then he has the kids pet and lick the cheetah well people gather around them.

Yeah Rex brought them to the Zoo to help the kids understand that not all animals are vicious animals but that some are friendly if you know how to handle the animal.