PHP variable for parent and child forums?

[WorldCraft]

I'm writing a few plugins that disable certain vB settings for certain forums. Instead of needing to write something like:
if ($GLOBALS[forumid] == forumparent1 || $GLOBALS[forumid] == forumchild1 || $GLOBALS[forumid] == forumparent2 || $GLOBALS[forumid] == forumchild2) {
$vbulletin->options[option_here] = 0;
...
}


For the sake of cleanliness/time-saving, is there a variable or method I could use to apply my plugin to all child forums of a given parent or parents?

Thanks!