Youthful chubbiness (5,3)

I believe the answer is:

puppy fat

(Other definitions for puppy fat that I've seen before include "Childhood plumpness" , "Adolescent flab" , "young blubber" , "Youthful plumpness" , "Childhood tubbiness, often lost by maturity" .)

I've seen this clue in The Times.

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