Tweening alpha, not affecting children?

I have a movieclip (holder) with 5 other movieclips inside it, these range from png images and other movieclips… but all 5 of them are in their own separate movieclip.

I tween the alpha of my holder mc from 0 to 1 (using tweenLite)… it doesn’t seem to have the same effect on the children movieclips inside it as it does the actual holder mc… for example one of my movieclips inside holder has a white background… you can see the white square around it whilst the holder movieclip is fading in despite the fact holder is a big white box.

Any one have any ideas why this is happening?