While I think this would be a nice idea and would certainly add colour and softness to their nests, my kids also have ideas of their own:
All mine go into a jar on the craft shelf,
even a haircut to make the hair the same length :)
the end result:
...with our native plants thriving and bringing birdlife to our suburban backyard, I am still tempted to get a hanging wire cage for the birds too. I'm sure the kids will share.