Child's train (4-4)
I believe the answer is:
choo-choo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">child's train</span>' is the definition.<br/ ><span class="explanation-format__explanation">(childish term for a train)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for choo-choo that I've seen before include "A baby's train" , "A child's train, sounds repetitive" , "Child's word for train" , "Chattanooga train?" , "Baby train?" .)