Merge CCSprites in one CCSrites

Hi,
How is it possible to merge some CCSprites in to one CCSprite at runtime?
Thanks.

I added CCSprites as child in to CCSprite like this:

CCSprite* pSprite = new CCSprite();
pSprite~~>init;
CCSprite* pSp1=CCSprite::initWithFile;
CCSprite* pSp2=CCSprite::initWithFile;
pSprite~~>addChild(pSp1);
pSprite->addChild(pSp2);

Bounding box of parent pSprite is (0,0,0,0)…
With is 0, Height is 0. May be i did something wrong?