that's probably because <% control Children %> returns a couple of Page class DataObjects, not Page_Controllers, meaning you have no access to methods in the children's controller. You could overcome this by creating a similar kind of method in the Page class itself. Feels a bit funny maybe, but ...
Thanks a lot, that helped.
I moved the function
public function getProductsList($num)
return $this->Products(Null, "Price,Title", Null, $num);
to the CategoryPage Class, so now it can be accessed from the ProjectsHolder template.
It works and I guess i shouldn't have problems with it set up like that...