My mom had these and she and I did lots of projects with them. As an all grown up girl, I find the present day fabric paints so much easier to use but that is me! I like being able to use brushes. Mom used to always bug me to keep the tips clean after a painting session, so that might be why you are having issues?
I googled "ball point fabric paints" and came up with a lot of links..here are a few:
http://www.createforless.com/Aunt+Ma.../pid78519.aspx
http://stores.ebay.com/Aunt-Martha-T...mbroidery.html
http://www.colonialpatterns.com/index.php?cPath=29
Looks like you and your grand kids can have lots of fun in the snowy new year days ahead! Happy Times!