Here's a nice article on all styles of jewelry from the Medieval period... maybe while you're reading it, it might give you some ideas:
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"Children had their own types of jewelry. References to children?s jewelry are quite early. Both noble families and wealthy bourgeoisie decorated children with brooches, chaplets, girdles. These were similar in fashion to those worn by the adults, if only cheaper and smaller in size. In Italy in the fourteenth century it was customary to give new-born babies crosses or pieces of coral to be worn round the neck, even more for the protection of the infant than as a decoration. The Child can be seen wearing a coral of this like in a number of quattrocento paintings of the Virgin and the Child." Maybe have the kids make a simple chain necklace with a piece of coral hanging down? This link to a woman's old website shows a pic of the August/Sept 2004 Bead & Button magazine, which has an article on "Sacred Embelllishment: A Look at Medieval German Bead Art", by Jen Segrest.
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- if you don't have that issue, I could try to find it for you as I'm sure I have it. :)))
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has a wonderful collection of pincushions! Seeing as how embroidery was so big back then, a pincushion made of felt and decorated with beads could be appropriate. I love the grinning cat face and eyeball pincushions. The girls could end up using their pincushions to hold any jeweled pins they have or maybe just stab it with pins when they're hit with teenage angst. :D But I think your Chainne Maille would be great for a 'girdle' or belt for the girls... just a loose chain for their waists, with a longer chain hanging down. Simple is best. :)