Milk containers (6)
(Another definition for cartons that I've seen is " Cardboard containers".)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">milk containers</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for churns that I've seen before include "Machines in which milk is beaten to make butter" , "Large milk containers" , "Beats or wihisks in milk containers?" .)