Snake right under child's toy (7)
I believe the answer is:
rattler
'snake' is the definition.
(rattler is a kind of snake)
'right under child's toy' is the wordplay.
'right' becomes 'r' (common abbreviation).
'under' says to put letters next to each other.
'child's toy' becomes 'rattle' (I've seen this before).
'r' put after 'rattle' is 'RATTLER'.
(Other definitions for rattler that I've seen before include "excellent specimen" , "US snake (colloq.)" , "I'm shaken!" , "Rickety old vehicle" , "Dangerous snake" .)