The command
<node3D>.getChildren() will return the list of children for an object that you have defined in the Vizard script. It will not return the list of sub-objects for that object as defined in the modeling software.
If you want to get a list with all sub-objects you could first get all the sub-object names and then use
<node3D>getChild() to get the handles to the sub-objects passing in their names. This prints out all sub-object names:
Code:
model = viz.add('gallery.ive')
for name in model.getNodeNames():
print name