Has their condition been diagnosed? Arthritis is very common in the wrist joint. The best thing for arthritis is range of motion exercises. As Karin mentioned stay away from bodyweight exercises supported on the wrists if this is painful. Pushups, for instance, or planks can be done with risers often eliminating the wrist pain. Strengthening the flexors and extensors of the hand may be helpful, but not necessarily of the forearm.