You can control the order of children by adding them in a
specific order. You can also control them as follows:
• By using the addChildAt() method to specify where
among the component’s children to add a child
• By using the setChildIndex() method to specify the
location of a specific child among a component’s
children in the display list
Note: As with the addChild() method, although the child
argument of the addChildAt() method is specified as
type DisplayObject, the argument must implement the
IUIComponent interface to be added as a child of a container.
All Flex components implement this interface.