playscene sprite kit random apparition of sprite

I have this code:

class PlayScene: SKScene {
let forest = SKSpriteNode(imageNamed: "forest")
let skeleton = SKSpriteNode(imageNamed: "skeleton")
let elf = SKSpriteNode(imageNamed: "elf")
let orc = SKSpriteNode(imageNamed: "orc")
let rand = Int(arc4random_stir())

override func didMoveToView(view: SKView) {
    print("Second view")
    self.forest.position = CGPoint(x: frame.size.width / 2, y: frame.size.height / 2)
    self.elf.position = CGPoint(x: 350, y: 300)
    addChild(self.forest)
    addChild(elf)
    print(rand)
    //if(rand >= 5){
        self.skeleton.position = CGPoint(x: 100, y: 300)
        addChild(skeleton)
    } /*else{
        self.orc.position = CGPoint(x: 100, y: 300)
        addChild(orc)
    }

}*/

Who works when he wants. And I don't understand why, I think is because of the relation parent/children, but I don't know what to change to not make them in conflict. Sometimes the elf appears, sometimes not, same for skeleton and orc... So I'm lost. Thank you for your help.