We really enjoyed our trip to Kidzania, a concept that was created in Mexico but which lends itself to anywhere where there are lots of kids!
Firstly, the cost. You'll pay a minimum 100 Dirhams per child to go in and be given some local money (yes, the kids have their own money too). Secondly, there's lots of activities for the kids to take part in, but there's often a long wait, especially at weekends (I'm talking about 30 minutes here). This is especially true for the popular rides like the airplane.
If you're looking for a full day experience with the kids, this is it. Come early (especially on a weekend), and be prepared to parent queue for the kids so that they don't have to wait.