Children's game lost by the witless (7)

I believe the answer is:

marbles

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'children's game' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for marbles that I've seen before include "You'll be mad if you lose them" , "Glass balls to play with" , "Small spheres of glass - statuary" , "Sculptures" , "alleys, perhaps" .)

I've seen this clue in The Guardian.

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