GetComponentsInChildren returns Component. Change to this:
var zombieLimbs: Component[];
zombieLimbs = gameObject.GetComponentsInChildren(Transform);
for(var limb :Transform in zombieLimbs){
// do something
}
NOTE: This code returns all transforms down in the hierarchy, including this object’s transform and all its grandchildren, if any. If you want only the child transforms, the code should be like this:
for (var child in transform){
// child in this case is Object - convert to Transform in limb:
var limb: Transform = child;
// do something
}