<?
ini_set('memory_limit','1000M');
$n = 100000;

$children = array();
for($i = 0; $i<$n; $i++)
{
  $children[$i]['f'] = array('sex' => rand(0,1),'day' => rand(0,6));
  $children[$i]['s'] = array('sex' => rand(0,1),'day' => rand(0,6));
}

foreach($children as $i => $child)
{
  if( ($child['f']['sex'] == 0 && $child['f']['day'] == 0) || ( $child['s']['sex'] == 0 && $child['s']['day'] == 0))
  {
    $condition[] = $child;
  }
}
echo "n: $n, sample size: ".count($condition)."\n";
foreach($condition as $child)
{
  if($child['f']['sex'] == 0 && $child['s']['sex'] == 0)
  {
    $both++;
  }
}
echo "both boys: $both\n";
echo "pct: ".$both/count($condition)."\n";
?>