Is it crazy to have a white sofa with children?

Not if you choose the right material. Fabrics like chenille or synthetic bouclé are very durable and washable, much more practical than pure cotton.

Does off-white go with pure white?

Yes, mixing different shades of white (snow, ivory, cream) adds depth and visual richness, preventing the space from looking "flat" or like a hospital.

Which decorative style fits best?

It's the perfect all-rounder. It works in Scandinavian style (with light wood), industrial style (softening the metal) or classic style (adding brightness).