A hot toddler we'd rocked to get asleep (4,2,3,5)
I believe the answer is:
dead to the world
'asleep' is the definition.
(thesaurus)
'a hot toddler we'd rocked' is the wordplay.
'rocked' indicates an anagram.
'a'+'hot'+'toddler'+'wed'='ahottoddlerwed'
'ahottoddlerwed' with letters rearranged gives 'DEAD TO THE WORLD'.
'to get' is the link.
(Other definitions for dead to the world that I've seen before include "Sound asleep; unconscious" , "Fast asleep" , "Sleeping" .)