Everyone included in blessing that's swell (7)
I believe the answer is:
balloon
'that's swell' is the definition.
(both can mean to expand or increase)
'everyone included in blessing' is the wordplay.
'everyone included' becomes 'all' (I've seen this in another clue).
'in' indicates putting letters inside.
'blessing' becomes 'boon' (synonyms).
'all' placed within 'boon' is 'BALLOON'.
(Other definitions for balloon that I've seen before include "Inflate" , "Bag filled with gas or air" , "See 21" , "Inflatable rubber bag, could be filled with hot air" , "Swell, increase rapidly" .)