Game crashes sporadically around checking for sprites - ios

Question

My game keeps crashing around this particular block of code.
The error message is Thread1: EXC_Bad_ACCESS(code =1) and the highlighted code is the following:
-(void)updateForArrays:(ccTime)delta
{
for (CCSprite *child in [self children]){
if (child.tag==2) {
if (CGRectIntersectsRect(child.boundingBox, _ship.boundingBox)) {
[self removeChild:child cleanup:YES];
_score += 1;
[_scoreLabel setString:[NSString stringWithFormat:#"Score : %d",_score]];
}
}if (child.tag ==3){
if (CGRectIntersectsRect(child.boundingBox, _ship.boundingBox)) {
CCScene *gameOverScene = [GameOverLayer gameOverScene];
[[CCDirector sharedDirector] replaceScene:gameOverScene];
}
}
}
}

Answer 1

You shouldn't modify ([self removeChild:child cleanup:YES]) collections (the [self children] array) while iterating. One way to go around this is to add objects for removal in a separate array and remove them after you're done checking for collisions.
Edit:
NSMutableArray *cleanupArray = [NSMutableArray array];
for (CCSprite *child in [self children]) {
// ...
[cleanupArray addObject:child]; // instead of [self removeChild:child cleanup:YES];
// ...
}
// actual removal of children
for (CCSprite *child in cleanupArray) {
[self removeChild:child cleanup:YES];
}
[cleanupArray removeAllObjects];

Answer 2

If all the children of self is of type CCSprite then your code will work. If not then you will face a crash. Because there is a chance that you might be forcefully typecasting a child which is of no CCSprite class. See if this code helps
-(void)updateForArrays:(ccTime)delta
{
for (id item in [self children]){
if((item isKindOfClass:(CCSprite class)])
{
CCSprite *child = (CCSprite *)item;
if (child.tag==2) {
if (CGRectIntersectsRect(child.boundingBox, _ship.boundingBox)) {
[self removeChild:child cleanup:YES];
_score += 1;
[_scoreLabel setString:[NSString stringWithFormat:#"Score : %d",_score]];
}
}if (child.tag ==3){
if (CGRectIntersectsRect(child.boundingBox, _ship.boundingBox)) {
CCScene *gameOverScene = [GameOverLayer gameOverScene];
[[CCDirector sharedDirector] replaceScene:gameOverScene];
}
}
}
}
}