Removing multiple children from the stage if the item is on stage - actionscript-3

Question

Good afternoon.
I'm making a game, and in games as you know, when you destroy an object, you must remove it from the stage.
My enemies have been added dynamically, via code and if the user goes back the enemy would still be in the display list.
I have attempted to remove enemies by trying this code.
removeChild(character); /removes player
removeChild(ground); // removes ground
childrenOnStage is a number which equals this.numChildren
for (var b:int = 0; b < childrenOnStage; b++)
{
if (getChildAt(b).name == "enemy")
{
removeChild(getChildAt(b));
}
}
When the user goes back to the main menu from the game, it runs this code.
The code loops though the all of the children on the stage, and those that have the name enemy should be removed.
But I get an error
[Fault] exception, information=RangeError: Error #2006: The supplied index is out of bounds.
My question is, how can I remove these enemies?
What if the enemy has been removed, this will cause more errors such as "null object" i.e enemy is not on stage, so why should I remove this enemy if it's not on?
Thank you.
Update due to Chernivs answer
//after adding all of the children, this must be updated last
childrenOnStage = this.numChildren;
private function fromLevtoStart(e:MouseEvent):void
{
if (e.target == backBtn1)
{
stage.removeEventListener(Event.ENTER_FRAME, level1)
stage.addEventListener(Event.ENTER_FRAME, mainGameLoop)
//container.removeChild(_character);
removeChild(character);
removeChild(ground);
for (var b:int = 0; b < childrenOnStage; b++)
{
if (getChildAt(b).name == "enemy")
{
removeChild(getChildAt(b));
//childrenOnStage --;
//update the variable below
childrenOnStage = this.numChildren;
}
}
this.gotoAndStop("Start");
}
}
This still doesn't remove all of the enemies, but only one for some reason.
it should loop through all of the children on stage that have the name enemy and remove them, but it doesn't.
After trying the asnwer below I can say that it only removes goblin1 which is named "enemy" and typ Goblin.
goblin1 = new Goblin();
goblin1.name = "enemy";
goblin2 = new Goblin();
goblin2.name = "enemy";
When I kill goblin1 it gets removed, then when I go back to the start screen goblin 2 doesn't even though that's the only goblin left with the name "enemy" it appears only goblin1 is targetted for some reason.

Answer 1

Instead of checking the name property, check the type of the display object. For example:
if(getChildAt(b) is Goblin) {
//remove
}

Answer 2

Basically, decreasing the variable should work. But if you get any problems with what you've removed, you can do this:
var enemies:Array = new Array();
for (var b:int = 0; b < childrenOnStage; b++) {
var child:DisplayObject = getChildAt(b);
if (child.name == "enemy") {
enemies.push(child);
}
}
trace(enemies);
See what you get. Loop through enemies and remove each of them - this way you won't need to decrease any variable nor think about numChildren - simply remove everything that is 'marked' as an enemy.