Having had lots of experiences in hospitals (as a volunteer and as a patient) I can totally see what Child's Play is for.
Hospitals are depressing places. The smell of disease is omni present. Its a bunch of boring walls, and you rarely hear anything other than machines beeping and children crying. Being sick is hard on a person. It is depressing, and in children, that feeling of boredom and powerlessness can really be harder than the disease itself.
Child's Play is unique. It tries to make hospitalization and disease easier for kids by taking their mind off of the disease. In the case of a kid with leukaemia, a game console can be the only entertainment they get between sessions of chemotherapy.
I can understand where giving to research charities seem to make more sense. In the future, a cure can prevent these long hospitalizations, however, today, as you will sit down in front of the television, keep in mind that in your local hospital, a kid is alone, in his hospital room, too weak to walk, or do anything else. What you take for granted is not easily accessible to these children.
Donate to the charity you want to donate to, but Child's Play is doing something extremely positive.