For a fun afternoon of skiing (and nothing too fancy) I can recommend the small ski resort at Bruchhausen / Olsberg. It’s only 1 hour 20 mins from Bielefield. It’s very much a family place and has a bunny slope with a pony lift alongside the main run. It’s not the Alps, but a good place for kids learning to ski (and a nice run for the adults). Winterberg is bigger ski resort 20 mins further away (more runs) and worth a visit too.