Marshals in the SCA use black-and-yellow staffs when supervising combat activities. The staff allows people to recognize the marshal, and may be used to signal the beginning of the fight, to call attention to the edge of the field, or to keep fighters from crashing into spectators.
You can make your own youth-marshal staff with a length of PVC/PEX and some black and yellow duct tape.
My preferred technique is to pull off a piece of each color of tape that is almost two times the length of the staff, stick them together with an overlap of half their width, then set them at a 60° angle to the pipe and wrap in a spiral.
(Depending on the size of your core, you might need to fiddle with the angle by a couple of degrees one way or the other, but that should give you even-sized stripes of both colors.)
When you reach the other end, cut the excess tape and fold the edges over.
It’s not beautiful, but it’s simple and cheap and it uses the same materials you already have on hand for weapon construction.