Sanford, the company that makes Sharpies, also makes a Laundry marker.
I've used both and don't see too much of a difference. I think if you
just stipulate to the parents to wash in cold water, you'll be okay. A
word of caution, though. The colors don't stand up to the test of time
as well as the black ones. I once did reindeer sweatshirts with the
kids. They stamped their thumbprints on each others' shirts and drew
the antlers on with brown sharpie, noses with red, name underneath with
black. A few kids came in the next week (after one washing) and had
lots of thumbprints and names but nothing else!