I'm debating this as well, mine is not 2 yet, but when the time comes.. I'm leaning towards a desktop, the ergonomics can be better (unless you consider a docke

I'm debating this as well, mine is not 2 yet, but when the time comes.. I'm leaning towards a desktop, the ergonomics can be better (unless you consider a docked laptop) and while it's a larger machine, it exposes a bit more of the complexity, and it'll be easy for us to take it apart to see what's inside and make changes/upgrades. There's also less possibility that he runs out with it and looses it or has it stolen, those are things he will learn in time, but for starters, I'll go with a desktop..