Theming "Add child" link

Sorry to open issue again. Thanks andreiashu to point to the right direction for adding child link in node.tpl.
It's working if you put parent_id manually. How you get parent id from current node? In my case I used:

print l("Add new child node", 'node/add/content_type', array('query' => array('destination' => 'node/[parent_id]/children', 'edit[parent]' => '[parent_id]')));

I'm getting link as following:

node/add/content_type?destination=node/[parent_id]/children&edit[parent]=[parent_id]

Any help will be appreciated.

Original post:

node/add/[node_type]?destination=node/[parent_nid]/children&edit[parent]=[parent_nid]
Where:
- [node_type] is the node type of the child you want to add
- [parent_nid] is the node id of the parent
- [parent] you let it as it is (literally)

For the l function you can write like this:
l("Add new child node", 'node/add/[node_type]', array('query' => array('destination' => 'node/[parent_nid]/children', 'edit[parent]' => '[parent_nid]')))