Small child's train? Half of it has defaced LNER glass (8)
I believe the answer is:
schooner
'glass' is the definition.
(schooner is a kind of glass)
'small child's train? half of it has defaced lner' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'child's train?' becomes 'choo choo' (childish term for a train).
'half of it' means to take half the letters (back).
'has' is a charade indicator (letters next to each other).
'defaced' means to remove the first letter (the word with its face removed).
'choochoo' cut in half is 'choo'.
'lner' with its initial letter taken away is 'ner'.
's'+'choo'+'ner'='SCHOONER'
(Other definitions for schooner that I've seen before include "Item used for drinking" , "No chores on this sailing ship" , "Sailing vessel - drinking vessel" , "Swift sailing vessel - sherry glass" , "Two-masted sailing ship" .)