Descendant takes everybody in for a little onion (8)
I believe the answer is:
scallion
'onion' is the definition.
(I know that scallion is a type of onion)
'descendant takes everybody' is the wordplay.
'descendant' becomes 'scion' (scion is a kind of descendant).
'takes' is an insertion indicator.
'everybody' becomes 'all' (I've seen this before).
'scion' enclosing 'all' is 'SCALLION'.
'in for a little' 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 scallion that I've seen before include "Vegetable" , "A spring onion with long neck" , "Spring 12" , "sort of onion" , "Green onion" .)