A 1" wide band of t-shirt, about 12" long. The band should stretch in the long direction.
A few scraps of wool felt, or vinyl, or other material that won't fray, cut into gem-like shapes.
A needle, or a sewing machine.
Unroll the t-shirt band, and pin one of the wool felt shapes to it. Sew just enough to attach the shape. Keep the stitching well shot of the edges of the band, so it can roll back up. Repeat this step, attaching the shapes evenly around the band. When all shapes are attached, give the band a little tug, so it will curl.
Wear wrapped as a bracelet, or unwrapped as a necklace. I had intended to show more pictures of the kids wearing these, but honestly, their hands and faces are rarely clean enough for close up photography. Now, to go make another, 3 bracelets are not easily divisible by 2 children.