Sounds like the power of a small child (4)
I believe the answer is:
mite
'a small child' is the definition.
(informal term)
'sounds like the power' is the wordplay.
'sounds like' shows a homophone (sound like).
'the power' becomes 'might' ('might' can be a synonym of 'power').
'might' sounds like 'MITE'.
'of' is the link.
(Other definitions for mite that I've seen before include "The widow's contribution, just in time" , "Arachnid; small child" , "The widow's small offering" , "Microscopic creature" , "Tiny creature found in food" .)