First off, that is an adorable project to be starting with children
. Well done on your innovative teaching method. I am a basketry nut x5y and I’ve been cobbing for 2y. Imagine how exciting it is to answer questions about a technique that combines two in one!
Second off I’d like to answer your question. As I was reading your post I instantly thought of natural hemp fibers. But then you mentioned nettle so you and I are thinking similarly about fine fibers for a tiny project. In order to scale it, nettle wouldn’t really be easy to source though. my idea for you is to cut up twine. Bonus if it’s hemp twine. You might get an aesthetic that is more pleasing with your paper clay if you were to use natural cotton and you can get a massive role of it if you buy cast padding. Another additive could be loose tinsel. I thought kids could like that. Or maybe even like friendship bracelet pieces, I don’t know I’m just trying to think outside the box for you
. Anyways, good luck and I sure sure would love to see what you come up with.