Gave a smack to child, entertaining sister, oddly (6)
I believe the answer is:
kissed
'gave a smack to' is the definition.
(smack can informally mean a kiss)
'child entertaining sister oddly' is the wordplay.
'child' becomes 'kid' (synonyms).
'entertaining' is an insertion indicator.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
The alternate letters of 'sister' are 'sse'.
'kid' enclosing 'sse' is 'KISSED'.
(Other definitions for kissed that I've seen before include "Osculated" , "Touched lightly" , "slightly touched" , "Bussed" , "Touched with lips" .)