capture the div tag event & height while minimizing and expanding

I'm using one parent Div Tag. Inside the parent div tag i'm using three child div tags. These three child div tags can be expanded or collapsed. If the child div tags are collapsed or minimized the parent div tag height wants to be reduced dynamically. How to achieve this using java script?

To me , If i'm minimizing the child tag the parent tag height is not getting reduced. I don't have any idea to fix that dynamically using java script.