Doubtless one of the youngest assemblies (6)
I believe the answer is:
creche
This clue could be a double definition.
'doubtless one' is the first definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'of the youngest assemblies' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for creche that I've seen before include "Place to leave children" , "A day nursery for child-minding" , "Daytime nursery" , "Day nursery for very young children" , "Representation of the nativity scene" .)