Son has ice cream or small cake (5)
I believe the answer is:
scone
'small cake' is the definition.
(I've seen this before)
'son has ice cream' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'has' is a charade indicator (letters next to each other).
'ice cream' becomes 'cone' (cone can refer to an ice cream cone).
's'+'cone'='SCONE'
'or' acts as a link.
(Other definitions for scone that I've seen before include "A little cake" , "Tea-time treat" , "Scottish location" , "Plain cake (for Scottish kings?)" , "The Stone of -----, returned to Scotland in 1996 after 700 years" .)