The perfect UI for what? If you say "computer", I strongly disagree, because a computer is a very general description for a variety of different machines.
Secondly, when we're talking about learning, using a command line will probably (definitely?) stimulate reasoning and abstract thinking, whereas you can emulate the effect of a touch screen with a door bell.
Addendum: Of course, you can emulate a keyboard with an iPad, but then what's the point? You even lose the tactile feedback a keyboard gives you.
I'd go out on a limb and claim that a kid will be better off by using actual water colors instead of a water color app on the iPad. In the same vein I think kids might have more important things to do at the age of three than typing commands into XMonad (not that it hurts if it's not the only thing they do).
In fact there are numerous studies that show the importance of practical and physical experiences for the development of abstract thinking, math etc. during early childhood.
Perfect UI compared to what the OP proposed would be the perfect UI.
I am not sure that many kids 2-5 get that much out of the command line. They are still working on building their visual skills, exploring tangibles etc.
I am all for command lines if the kid get it, just think it's rare that they get that much out of it in that young age.
Touch screens are interesting because they build on the sorts of visual skills that we use in daily life. The command line is interesting because it nurtures skills you can't get from wandering around a garden. If I want a child to build their visual skills, I want to get them out in nature, or playing with physical toys, not a touch screen.
A CLI on the other hand is a very good abstract reasoning thing - it's on the same level as teaching a kid to read, or counting. And like reading I think it's a very valuable exercise whether the kid "gets" it or not.
It's only good for abstract reasoning if you can manipulate it and understand what you are doing. Kids at that age can't manipulate it the way you seem to suggest. They can "only" (if I do X, Y happens). It takes pretty intelligent kids to be able to be creative about that at such a young age.
The iPad on the other hand allows for emulating the reality the kids know and thus allow them to play around and learn abstraction based on where they are mentally.
Secondly, when we're talking about learning, using a command line will probably (definitely?) stimulate reasoning and abstract thinking, whereas you can emulate the effect of a touch screen with a door bell.
Addendum: Of course, you can emulate a keyboard with an iPad, but then what's the point? You even lose the tactile feedback a keyboard gives you.
I'd go out on a limb and claim that a kid will be better off by using actual water colors instead of a water color app on the iPad. In the same vein I think kids might have more important things to do at the age of three than typing commands into XMonad (not that it hurts if it's not the only thing they do).
In fact there are numerous studies that show the importance of practical and physical experiences for the development of abstract thinking, math etc. during early childhood.