I'm iterating over an array of nids. Now I need to check whether the current nid is a child (in the menu) of the current menu object. But i could find any method to get all children of a node by nid. (something like menu_get_children($nid);)
Has anyone an idea how to do that? (quick and dirty is allowed)
I don't think there is an easy way to do that. Nodes do not form a hierarchy (Unless you are using the book.module), there is no real connection between menu links and nodes.
When you look at http://api.drupal.org/api/drupal/modules--menu--menu.module/function/menu_node_prepare/7, the only way to get the menu link belonging to a node is to look for a menu link with the path "node/nid".
You could try to do the same thing and then get the menu childrens of that, then again check if they point to a node and extract the nid from the link_path.
