Playthings lost by people not all there (7)

I believe the answer is:

marbles

I'm a little stuck... Click here to teach me more about this clue!

'playthings' is the definition.
(I know that marble is a type of playthings)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for marbles that I've seen before include "Small spheres of glass - statuary" , "Game with alleys and taws" , "Sculptures" , "Mind" , "alleys, perhaps" .)

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