Thanks Splittingred.
Was trying to use all kinds of derivations within my getresources call including &tpl_{second}, &tpl_{2}, &tpl_{2nd} etc.
Did what you suggested and my site works. Not sure that my terminology is correct, but this use of the &tpl_{n} property is a great way of iterating resources from the same parent in circumstances where the output is styled by different css classes.
This is my snippet call in the main template:
[[!getResources? &parents=`3` &limit=`4` &tplFirst=`articleheadline` &tpl_2=`articlesnextheadlines1` &tpl_3=`articlesnextheadlines2` &tpl_4=`articlesnextheadlines3` &includeContent=`1` &sortby=`createdon` &showHidden=`1` &sortDir=`DECS`]]