Second child loves snowmobile (6)
I believe the answer is:
skidoo
'snowmobile' is the definition.
(trademark name for a type of snowmobile)
'second child loves' is the wordplay.
'second' becomes 's' (common abbreviation).
'child' becomes 'kid' (synonyms).
'loves' becomes 'oo' (love means 0 in tennis).
's'+'kid'+'oo'='SKIDOO'
(Other definitions for skidoo that I've seen before include "Motorised toboggan - get out fast" , "snowmobile" , "winter vehicle" , "Snow vehicle with skis at the front" , "Motorised sledge" .)