How can I check how many movieClips exist in a container

Hi,

How can I check how many movieClips exist in a container and how much space are they taken?

In other words, how can I make this calculation if I have a rectangular movieClip (containerMc) that is 5x1px and five square movieClips (sq1Mc,sq2Mc, sq3Mc, sq4Mc and sq5Mc) that are 1x1px and which can dynamically be placed inside containerMc and I want to know how many and which of these five movieClips already exist in containerMc so I can determine where the next square movieClip needs to be placed?

Can someone be so kind and show me how to do this or direct me where I can find the answer?

Thanks a lot!