Modelling clay allows children to have a 3D art activity in hospital. This gives them something different from the 2D drawings and art activities they usually do. It gives them a new way to be creative.
Play Doh (if it's new and hasn't had a chance to get too hard yet) is easy to use if your child is feeling sick or tired. It can also be used in bed as long as there is a bedside table to play on. (Most hospital rooms will have a movable bedside table for each bed.)
The next step up from Play Doh is Model Magic. When this dries it can be decorated with markers or items like yarn or feathers. This adds a new creative element to modelling which will work well when your child is in hospital.
Picture: Dragonfly made with Model Magic and other Crayola supplies.