CCMenu child of child selector not firing - cocos2d-iphone

Question

I have a ccmenu with a ccmenuitemsprite in a ccmenuitemsprite which has the selector.
I wish for the child of child to be a play button that fires a selector but its not firing.
CCMenu *menu [CCMenu menuWithItems: nil];
CCMenuItem *bg = [CCMenuItemSprite itemFromNormalSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(0,50,100,100)]
selectedSprite:nil
disabledSprite:nil
target:self
selector:nil];
CCMenuItem *playBtn = [CCMenuItemSprite itemFromNormalSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(0,0,50,50)]
selectedSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(50,0,50,50)]
disabledSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(100,0,50,50)]
target:self
selector:#selector(onPlay:)];
[bg addChild:playBtn];
[menu addChild:bg];
[self addChild:menu];

Answer 1

If you want to pass the name of your images as arguments, please use the following code:
CCMenuItem *playBtn = [CCMenuItemImage itemFromNormalImage:#"image.png"
selectedImage:#"image_selected.png"
disabledImage:#"image_disabled.png"
target:self
selector:#selector(onPlay:)];
The constructor you are using is expecting a CCSprite, not an NSString.
OK, after you edited the answer, I looked more closely, and you have the playBtn as a child of bg. You can't do that. Only the direct children of CCMenu are able to send callbacks:
[menu addChild:playBtn];
I would suggest you do this actually:
CCMenuItem *playBtn = [CCMenuItemSprite itemFromNormalSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(0,0,50,50)]
selectedSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(50,0,50,50)]
disabledSprite:[CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(100,0,50,50)]
target:self
selector:#selector(onPlay:)];
CCMenu* menu = [CCMenu menuWithItems:playBtn, nil];
CCSprite* bg = [CCSprite spriteWithFile:#"sprite_sheet.png" rect:CGRectMake(0,50,100,100)];
[self addChild:bg];
[self addChild:menu];