Baby initially nursed by two parents, one with fangs (5)
I believe the answer is:
mamba
'one with fangs' is the definition.
'baby initially nursed by two parents' is the wordplay.
'two parents' can mean two replacements for 'parent'.
'initially' indicates taking the first letters.
'nursed by' is an insertion indicator.
'parent' becomes 'ma' (ma is a kind of parent).
'parent' becomes 'ma' (ma is a kind of parent).
The first letter of 'baby' is 'b'.
'ma'+'ma'='mama'
'b' going into 'mama' is 'MAMBA'.
(Other definitions for mamba that I've seen before include "One's venomous" , "Venomous African tree snake" , "Venomous snake; rhymes with dance" , "Snake that might kill" , "It may be deadly" .)