You can create a group node for this:
Code:
import viz
import vizact
viz.go()
group = viz.addGroup()
soccerball = viz.addChild('soccerball.osgb',pos=[-0.5,1.8,1.5],parent=group)
basketball = viz.addChild('basketball.osgb',pos=[0,1.8,1.5],parent=group)
volleyball = viz.addChild('volleyball.osgb',pos=[0.5,1.8,1.5],parent=group)
vizact.onkeydown(' ',group.visible,viz.TOGGLE)