Toys of the Eighties, Crib Gyms
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These contraptions were big in 80s nurseries, day cares, etc. The toy consisted of various rattlers, grippers, sqeakers, etc. which dangled from a strap strung across the rails of a crib so that babies who could not sit up yet could keep themselves entertained while their caregivers watched TV, took naps, whatever. You don't see them anymore because too many kids got themselves dangerously tangled, strangled, dangled, etc. at some point during the play process. There were a lot of different styles put out by various companies, including THIS particularly gaudy version by Fisher Price (see photo).
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