These are consumers, not just students, they have purchased a product which is the education being provided by the school. If they want to fuck off and not pay attention let them, it's their wasted money. As long as they aren't bothering other people, there's no problem. You can ban everything and they will still fall asleep if they are bored. Stop treating them like children. If the info in the lecture is so important that they have to pay attention they will catch on quickly, if it isn't then the teacher sucks.

But you are framing the idea as if the choices are 1. No computer at all
or
2. Only computers and no playing with anything else

Which is silly and clearly not what a reasonable person would do.
I have 4 kids and all of them do the positive things you mentioned, they read (not the baby) climb, draw, build, etc. but they also write games using MIT's SCRATCH, and lately Google app builder.
http://www.youtube.com/watch?v=4q9kcr1Et3s
They are doing these things because they find them fascinating and kids are curious critters. As a parent it's my job that they do these things in a healthy way. As for a toddler and iPad is a great thing for them to play with, but it certainly shouldn't be the only thing that they play with. The touch screen removes the abstraction of an input device and people are starting to make some interesting games to play.
http://www.youtube.com/watch?v=8RKQwwetcQw
Playing games with your toddler on the iPad is fine, it's also fine that you choose not to. But it is about making it a tool in your suite of parenting tools and using it when it makes sense, not as a baby sitter.

Are you guys on crack? The iPad is like a gift from the gods for toddlers. It removes the abstraction of an input device entirely. They touch what they want to interact with. Check out the video of my 22 month old playing with an iPad: http://www.gonzoparents.com/2010/08/app-review-animal-hide-and-seek.html It's not spam, it's on topic!