Unnerve with baby's toy (6)
I believe the answer is:
rattle
I believe this is a double definition.
'unnerve' is the first definition.
(thesaurus)
'baby's toy' is the second definition.
(I've seen this before)
'with' is the link.
(Other definitions for rattle that I've seen before include "Baby's toy; irritate" , "Child's toy or kind of snake" , "Let rat make the sound" , "flap" , "led to Tweedledum and Tweedledees quarrel?" .)