Son fibs about 500 items in playground? (6)
I believe the answer is:
slides
'items in playground?' is the definition.
(playgrounds often have slides)
'son fibs about 500' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'fibs' becomes 'lies' (informal term for lies).
'about' indicates putting letters inside.
'500' becomes 'D' (Roman numeral for 500).
'lies' enclosing 'd' is 'lides'.
's'+'lides'='SLIDES'
(Other definitions for slides that I've seen before include "Slips, slithers" , "Pieces of glass for study of specimens" , "Sloping chutes in the playground" , "Pieces of glass under the microscope" , "Sloping chutes in playgrounds" .)