Youngster left on high peak -- son's escaped (7)
I believe the answer is:
leveret
'youngster' is the definition.
(I've seen this before)
'left on high peak son's escaped' is the wordplay.
'left' becomes 'l' (common abbreviation**).
'on' means one lot of letters go next to another.
'high peak' becomes 'everest' (I've seen this before).
'escaped' suggests deleting specific letters.
'everest' with 's' taken out is 'everet'.
'l'+'everet'='LEVERET'
(Other definitions for leveret that I've seen before include "Baby hare" , "Fast runner, potentially" , "Young three dn" , "First-year hare" , "youngster in form" .)