It's lucky mother's gone to bed (6)
I believe the answer is:
mascot
'it's lucky' is the definition.
I know that 'lucky' relates to this answer.
'mother's gone to bed' is the wordplay.
'mother's' becomes 'mas' (Ma is another word for mother or mum).
'gone to bed' becomes 'cot' (I can't justify this - if you can you should give a lot more credence to this answer).
'mas'+'cot'='MASCOT'
Can you help me to learn more?
(Other definitions for mascot that I've seen before include "Thing considered to bring good luck" , "Good luck token" , "Something considered to bring good luck" , "Does it get you first place" , "Character or object used to bring good luck, or represent an organisation" .)