In a childish manner (10)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">in a childish manner</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know this)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for childishly that I've seen before include "in puerile manner" , "In an immature fashion" , "Like baby" .)