Child’s donkey loses head, creating current disturbance (4)
I believe the answer is:
eddy
'current disturbance' is the definition.
'child's donkey loses head' is the wordplay.
'child's donkey' becomes 'Neddy' (Neddy the Donkey, character in children's books).
'loses head' means to remove the first letter.
'neddy' with its initial letter taken off is 'EDDY'.
'creating' is the link.
(Other definitions for eddy that I've seen before include "religious leader" , "Christian Scientist" , "Water circulating" , "current revolution" , "Fellow" .)