Bottle child found under vehicle (6)
I believe the answer is:
carboy
'bottle' is the definition.
(I've seen this before)
'child found under vehicle' is the wordplay.
'child' becomes 'boy' ('boy' can be a synonym of 'child').
'found under' means one lot of letters go next to another.
'vehicle' becomes 'car' (car is a kind of vehicle**).
'boy' put after 'car' is 'CARBOY'.
(Other definitions for carboy that I've seen before include "Large bottle for holding corrosive liquids" , "Large bottle to contain chemicals - boa cry (anag)" , "Large round bottle in wicker casing" , "Large round bottle surrounded by framework" , "Large glass container" .)