Shattered toddler with a ted, who is fast asleep (4,2,3,5)
I believe the answer is:
dead to the world
'fast asleep' is the definition.
(I've seen this before)
'shattered toddler with a ted who' is the wordplay.
'shattered' is an anagram indicator.
'with' is a charade indicator (letters next to each other).
'toddler'+'a'+'ted'+'who'='toddleratedwho'
'toddleratedwho' anagrammed gives 'DEAD TO THE WORLD'.
'is' is the link.
(Other definitions for dead to the world that I've seen before include "Fast asleep" , "Sleeping" , "Sound asleep; unconscious" .)