Scaling all nodes of an object together in sceneKit - swift

Question

I'm using apple' approach to handle AR in sceneKit, and here I use this method to scale the object, it works fine when all the nodes of the object merged into one node, but because of the object's animations, I can't make all into one node. So Need to change this method differently that I can scale all the nodes together.
Can anyone help me on that? Thanks
var trackedObject: VirtualObject? {
didSet {
guard trackedObject != nil else { return }
selectedObject = trackedObject
}
}
#objc func pinched(_ gesture :UIPinchGestureRecognizer) {
switch gesture.state {
case .began:
gesture.scale = isScaledChanged ? CGFloat(trackedObject?.objectScale.x ?? 1) : CGFloat(1)
case .changed:
var newScale: SCNVector3
if gesture.scale < 0.5 {
newScale = SCNVector3(x: 0.5, y: 0.5, z: 0.5)
} else if gesture.scale > 3 {
newScale = SCNVector3(3, 3, 3)
} else {
newScale = SCNVector3(gesture.scale, gesture.scale, gesture.scale)
}
isScaledChanged = true
trackedObject?.objectScale = newScale
default:
break
}
}
and in the VirtualObject class
var objectScale: SCNVector3 {
get {
return childNodes.first!.scale
}
set (newValue) {
childNodes.first!.scale = newValue
}
}
I did something like that, but didn't work well
var objectScale: SCNVector3 {
get {
for node in childNodes {
return node.scale
}
return childNodes.first!.scale
}
set (newValue) {
for node in childNodes {
node.scale = newValue
}
}
}