Vessel more readily allowing first couple of children on board (8)
I believe the answer is:
schooner
'vessel' is the definition.
(type of ship)
'first couple of children on board' is the wordplay.
'first' becomes 'sooner' (I've seen this in another clue).
'couple of children' becomes 'ch' (I can't explain this - if you can you should believe this answer much more).
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'sooner' enclosing 'ch' is 'SCHOONER'.
'more readily allowing' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for schooner that I've seen before include "Type of glass" , "boat" , "Sailing vessel used in former times" , "Swift sailing vessel - sherry glass" , "wooden vessel" .)