It's difficult to say what you are doing wrong without seeing any code. The following sample applies a clip plane to a root node and affects all children. It works for me in Vizard 3 and 4:
Code:
import viz
viz.go()
root = viz.addGroup()
for x in range(20):
viz.add('logo.ive',pos=(0,0,x),parent=root)
root.clipPlane([1,0,0,0])
import vizcam
vizcam.PivotNavigate(distance=10)
Also, in the future please post questions in new threads.