Frixion Fine Point Clicker Pens - Assorted 3 Pack
Package of 3 retractable pens in pink, purple and turquoise with a fine 0.7mm tip.
Markings disappear with heat (thermo-sensitive gel ink). The cap has a rubby thing you can use to erase the mark, but an iron works better on fabric.
Test marker on scrap fabric to make sure it will disappear.