Grabbing all Children and components of those children

These examples will use tranform (the current game objects transform), but can be applied to the transform of any other game object just as easily.

 //Looping though the children
 foreach (Transform child in transform) {
     // do whatever with child 
 }

 //Creating a list of children
 Transform[] children = transform.Cast<Transform>().ToArray();

 //Creating a list of components attached to the children
 Component[] componentsOfChildren = transform.GetComponentsInChildren<Component>();

Note that these techniques are only searching one level deep, they would need to be applied recursively to find grandchildren etc.