"All kids should grow up today like I did when I was a kid!" - Said everyone ever
Following the above logic, my kids will be forced to grow up on a 386 running DOS and several shareware games. Later, I will upgrade them to Windows 3.11.
Basically throughout adolescence, on various computers, they will have to reinstall Windows 95 78 times, Windows 98 174 times, Windows NT 4.0 14 times, Windows 2000 52 times, and Windows XP 739 times. This will be their chore, along with mowing the grass and whatnot.
It won't be until they are legal adults at 18 years old that they will be allowed to touch anything recembling a modern computer.
All sarcasm aside, I think a good exercise would be to ask a kid to, to the best of their ability, to present a compelling written arguement for why they *want* that particular computer. It could be a powerpoint explaining it's uses compared to other computers, it could be an excel showing the cost/benefit, it could be a song. Grade them on it taking into account their age. The exercise would force them to really think it though, I would hope. It would also prevent acting on impulse, and it would teach critical thinking. At the end of the day, no computer will ruin a good kid.