Cause of some childhood ups and downs (6)

I believe the answer is:

seesaw

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'ups and downs' is the definition.
(thesaurus)

I don't understand the remainder of the clue.

(Other definitions for seesaw that I've seen before include "Child's plaything with plank over barrel" , "Teeter-totter" , "Piece of playground equipment" , "swing" , "It goes up and down with the child" .)

I've seen this clue in the Evening Standard.

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