Tetherkid trolley

Many is the time I've been at a supermarket, watching some distressed person trying to keep their trolley, two 4-year olds and their temper under control. There are, of course seats in the trolleys, but if you put an actual child in it, you have to armor-plate the shopping compartment, so nothing gets played with. My idea would be to have a crate or harnesses, similar to those used by climbers, but child-sized, next to the entrance. each harness is attached to a trolley with the same key thing the trolleys have on the handlebar, only these are located on the side of the trolley. the strap on the harness is short enough, so that two kids could not reach around the trolley to squabble. If this is unacceptable to anyone, the can simply show their kid a harness and say that all the bad children have to wear them.