setHardness is a method of VizPhysicsShape, not of VizNode/VizChild. Check the example again. In addition, the case of the letters in the method mater.
Code:
ball = viz.add('ball.wrl')
shape = ball.collideBox()
shape.setHardness(.5)
As we see here, setHardness is called on the object that returns from the collideBox() function. This is because you can have multiple collide shapes assosated with one node, such as the ball.
Check out this code to see multiple collide shapes:
Code:
box = viz.add('box.wrl')
box.collideBox()
ball = box.add('ball.wrl')
ball.scale(2,2,2)
ball.translate(0.5,-0.5,0)
box.collideSphere(pos=(0.5,-0.5,0))