If you look close the problem becomes quickly Apparent....at least to me
Just beyond the fence, between the fence and the moat wall, there is vegetation that is grown up and dense. The kid was taken to the zoo and to see the gorilla but couldn’t. At his height, his view was blocked by the bushes. Not to worry he thought, I’ll climb up the fence. Still can’t see, I’ll climb over the fence. He went a step too far and off the moat wall cliff
That’s not it - he wanted to go into the water. And wasn’t used to being told no and having his mother mean it.