Selling online and in shops for as little as seven yuan ($1), so-called toothpick crossbows were originally designed to shoot out just that -- toothpicks.
But if swapped out for needles they are potent enough to crack glass, said the Shanghai Daily newspaper, quoting shop owners as saying they were selling out of the "toys" fast and struggling to meet demand.
Other Chinese state media said the mini crossbows can fire at a distance of more than 20 metres (65 feet) and shoot iron nails in place of toothpicks.
"The 'Toothpick Crossbow' toy has spread across China like wildfire among the nation's primary and middle school children," said the Shanghai Daily.
"The unusual shooting toy may be very small but it is powerful enough to puncture a balloon and pierce cardboard. And when the toothpick is swapped for a metal needle it becomes a dangerous weapon."
Police in Chengdu, a major city in China's southwest, have reportedly stopped sales of the product and concerned parents across the country want the government to issue a nationwide ban.
"Hurry up (and ban them), pupils do not understand and are just shooting people for fun. It will cause accidents sooner or later," one parent wrote on Weibo, China's Twitter-like website.
Another worried onlooker wrote: "Our primary school began to investigate this from Monday and they're very dangerous."