var parentNode = SKNode()
var childNode1 = SKSpriteNode()
var childNode2 = SKSpriteNode()

self.addChild(parentNode)
parentNode.addChild(childNode1)
parentNode.addChild(childNode2)

for child in parentNode.children as! [SKNode] {
    // ...
}

for child in parentNode.children {
    if let spriteNode = child as? SKSpriteNode {
        // ...
    }
}

for case let child as SKSpriteNode in parentNode.children {
    // ...
}

let children = parentNode.children
for child in children {
    // Do something.
}

for case let child as SKSpriteNode in parentNode.children {
    // ...
}

let a = Date()
    for case let s as SomeSpriteClass in children { k += 1 }
    let t1 = a.microseconds()

    let b = Date()
    for s in spaceships { k += 1 }
    let t2 = b.microseconds()

    print("(t1) (t2)")

939 43
140 33
127 33
117 37
109 30
126 33
127 33
109 29
96 30
96 29
99 30
97 30
97 30