Is there any informal term used by children for this kind of pens used for drawing? (In BrE, please)
How about felts?
It's now thirteen years since I worked with British pupils/students (11-18), so my contribution may appear dated.
Way back then (), unless someone particularly wanted to specify exactly what sort of writing tool they were referring to, pen covered: felt tips (large and small), fountain pens, ball-point pens (biros to my generation), board markers, magic markers, the thingies that you touched a computer screen with, etc.