Misfortune of child seen regularly in play (8)
I believe the answer is:
accident
'misfortune' is the definition.
(accident is a kind of misfortune)
'child seen regularly in play' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'in' is an insertion indicator.
'play' becomes 'act' (synonyms).
'child'+'seen'='childseen'
The alternate letters of 'childseen' are 'ciden'.
'ciden' inserted into 'act' is 'ACCIDENT'.
'of' acts as a link.
(Other definitions for accident that I've seen before include "Prang" , "Pile-up" , "Eg, car crash" , "Unforeseen mishap" , "Unexpected and unplanned event" .)