LAST weekend in Fair Harbor, N.Y., on Fire Island, a few dozen children gathered on the boardwalk for the local tradition of selling lemonade, baked goods and painted seashells to passers-by at sunset. Among the children was Julia Colen, a 12-year-old vacationer from New Jersey, who in addition to hawking cupcakes and drinks was presiding over a stand overflowing with brightly colored bracelets. Julia and a friend had made the jewelry out of tiny rubber bands, using a crafts kit called Rainbow Loom.

“We had a lot, at least 100,” Julia estimated of their inventory, which they priced at $1 to $2 apiece. Sales were impressive that night — “we made like $68,” she said.

Julia is among hundreds of thousands of youngsters — and parents — in the United States who are using Rainbow Loom. The kit consists of two plastic template boards, a hook, 24 plastic clips and 600 multicolored mini rubber bands. From it, 24 bracelets can be woven into patterns similar to those traditionally used in lanyards and friendship bracelets, but more complex and colorful.

Rainbow Loom is the invention of Cheong Choon Ng , a Malaysian immigrant of Chinese descent with a graduate degree in mechanical engineering. He came up with the idea in 2010 and began selling the kit while employed as a crash-test engineer for Nissan.