Im using this module for a site for someone whos going to create lots of content. They will first create a parent node then a few children nodes.

At the moment they have to create the nodes separately, and then either choose the parent or child. Could I make it so a user would create the parent node first, then then have a link to create a child node with the parent node automatically selected as the parent?

Looking at the post from the link below it seems like this module used to / can work like this.

http://drupal.org/node/294508
The simplest way to handle this is actually to reverse the process - go to the parent node, click the children tab and create a new child of the appropriate type. That will create a new child with the appropriate parent already chosen.
We've got oodles of sites with significant content, and that's how we do it. That's a change to your process, but you can use it to get the job done right now.
Thanks