Ties top of overshoe to upset child's foot (7)
I believe the answer is:
tootsie
'child's foot' is the definition.
(childish term for a foot)
'ties top of overshoe to upset' is the wordplay.
'top of' indicates taking the first letters.
'upset' indicates an anagram.
The initial letter of 'overshoe' is 'o'.
'ties'+'o'+'to'='tiesoto'
'tiesoto' with letters rearranged gives 'TOOTSIE'.
(Other definitions for tootsie that I've seen before include "Funnily enough, foot" , "Child's word for toe" , "Foot (jocular)" , "Film with Dustin Hoffman" , "What's furthest from a child's mind" .)