It’s a 21st century spin on a traditional childhood.

The hottest device among tweens these days isn’t an iPhone or Nintendo Switch, but fidget spinners that typically sell for less than $20. Often made of plastic or metal, these are ball-bearing toys originally used as a medical tool for kids to release nervous energy, as their name suggests. They’ve suddenly found their way into school yards across the country as kids find themselves spinning the little gadgets to ward off boredom.

The eldest son of Manhattan mom Lyss Stern came home a few weeks ago demanding that she immediately accompany him to a toy boutique to pick up a spinner. She acquiesced, in part because her 13-year-old was more enthusiastic about it than when making requests for pricier tech gadgets. “I’m all for going off the grid,” says the chief executive of Divalysscious Moms, a marketing and events agency for mothers and author of new book “Motherhood is a B#tch!.” “I figure if they spend more time off their iPhones or iPads, that’s a good thing.”

Stern doesn’t regret her purchase, saying that playing with the toy calms and de-stresses her two older kids, who now have four fidget spinners between them. “Children have a lot of energy” so this is a good way to let it out, says Stern.

Of course, kids being kids, they’re always find new and surprising ways to improvise the toys. For example, Stern’s 13-year-old has found a way to balance the fidget spinner on his nose. Many other tweens have also turned to sharing Instagram and Snapchat videos showing off their spinning skills. Stern doesn’t mind this particular use of technology: she’s looking forward to her kids buying her a pink spinner of her own.

Occupational therapists have long used similar devices to treat kids with some variation of ADHD, ADD or what they call sensory processing disorder, a condition in which certain stimuli aren’t detected or organized so that the right response is triggered. So while there’s evidence that fidget spinners are useful for kids, some have concerns about them being so casually used.

“It needs to be monitored,” says Sandra Schefkind, pediatric program manager at the American Occupational Therapy Association. “We are all diverse learners so tools should be customized rather than one-size-fits-all. Hopefully, the toys are used with educators and occupational therapists as part of the team.”

The danger is that some children may be overstimulated from the spinners. “For some children it works very well,” says Varleisha Gibbs, chair and director of graduate programs in occupational therapy at Wesley College in Delaware. However, she notes that the spinners largely trigger visual stimuli, whereas certain kids may need a gadget that’s more tactile. “In some cases, the spinner may overwhelm the part of the brain that processes sensory information.”