Dear toddler regularly gets crumble (5)
I believe the answer is:
erode
'crumble' is the definition.
(I know that erode is a more specific form of crumble)
'dear toddler regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'dear'+'toddler'='deartoddler'
The alternate letters of 'deartoddler' are 'ERODE'.
'gets' is the link.
(Other definitions for erode that I've seen before include "Wear away with weather" , "'Deteriorate, wear away (5)'" , "Grind down" , "go to pieces!" , "Slowly remove" .)