Make a teddy bear out of then. Or a throw.
Ruth....Cut them out and make a throw.
I also love the blanket idea or a pillow case!
Pillows would be fun or a small quilt. For holiday memories you could make an ornament.
You can cut them down to a manageable size, sew the arms, leg and neck holes closed and stuff them into pillows.
A stuffed animal with a patch sewn to it of make the stuffed animal depending on the material. Maybe an embroidered message would make it more personal.
You could cut up and make a rug by joining strips together and crocheting in a circle or oval etc. or cut pieces into oblongs and using sacking as a backing and a rug needle or rachet make a soft rug.
You could make a collage picture, if the sweats have designs on them using Mod Podge to stick them onto a backing. Maybe along with photos or in the shape of something they took interest in. ( stick the pieces on a backing and lay over a cutout that represents the person eg: Motorbike or Horse or Car or Butterfly, Flower basket etc. Hope that is of help.
\\you could also stick strips around a mirror or picture too.