A childish beast (5)

I believe the answer is:

bunny

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'a childish beast' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

This is all the clue.

Can you help me to learn more?

(Other definitions for bunny that I've seen before include "Child's term for a burrower" , "pet!" , "Young rabbit" , "Child's word for rabbit" , "Bugs this" .)

I've seen this clue in the Evening Standard.

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