Character will signal agreement with daughter, unknown (5)
I believe the answer is:
noddy
'character' is the definition.
(I have seen 'childish character' mean 'noddy' so perhaps 'character' could also mean 'noddy')
'will signal agreement with daughter unknown' is the wordplay.
'will' says to put letters next to each other (I've seen this in other clues).
'signal agreement' becomes 'nod' (I've seen this in another clue).
'with' means one lot of letters go next to another.
'daughter' becomes 'd' (genealogical abbreviation).
'unknown' becomes 'y' (algebra).
'nod'+'d'='nodd'
'nodd'+'y' is 'NODDY'.
(Other definitions for noddy that I've seen before include "Toytown character" , "childish character" , "Sea bird" , "Blyton's Toytown boy" , "Simpleton; oil rig" .)