SELECT `id` FROM `table` WHERE `published`='1' AND ( `parent` = '1' OR `parent`='2')
$c= $modx->newQuery('modResource', 'web');
$c->select('id');
$c->where(array(
'`modResource`.parent' => 1,
));
$c->orCondition(array(
'`modResource`.parent' => 2,
));
$c->andCondition(array(
'`modResource`.published' => 1,
'`modResource`.context_key' => 'web',
));
$collection = $modx->getCollection('modResource', $c);