Removing child via hitTestObject

Question

Before i ask what im sure will be a very silly question, let me say that i am a total beginner at Action Script. I am trying my best to make a simple game for University, and i have tried, but cant figure it out.
Anyway, the game is basically Breakout, where you control a Paddle, and try to hit a ball towards blocks.
I cant figure out how to remove the blocks when the ball hits them.
I have got this so far -
if (ball.hitTestObject(b3)) {
    yDirection *= -1;
    stage.removeChild(b3)
Where b3 is block number 3. (I have 6 blocks, b1 - b6, respectively).
This works for the first time the ball hits the block; the block dissappears and the ball bounces back. However, when the ball travels over this area again, it crashes and i get an error.

Answer 1

So, i would put -
var brickA:Array=[];
var tl:MovieClip=this;
for(var i:int=0;i<6;i++){
tl["b"+(i+1)]= new brick();
brickA.push(tl["b"+(i+1)]);
addChild(tl["b"+(i+1)])
tl["b"+(i+1)].x=5+i*(tl["b"+(i+1)].width+10);
tl["b"+(i+1)].y=100;
for(var i:int=brickA.length-1;i>=0;i--){
if(ball.hitTestObject(brickA[i]){
brickA[i].parent.removeChild(brickA[i]);
var temp = brickA[i];
brickA.splice(i,1);
temp=null;
Im sorry im being an idiot about all this