Baby’s toy causing alarm (6)
I believe the answer is:
rattle
This clue is a double definition.
'baby's toy' is the first definition.
(I've seen this before)
'alarm' is the second definition.
(rattle can mean to alarm or unnerve)
'causing' is the link.
(Other definitions for rattle that I've seen before include "Baby's toy - conductor" , "Put out" , "Child's toy or kind of snake" , "Warning given by deadly snake" , "Noisy type of snake" .)