So as usual: "go ask real hardware forums", "you wouldn't go to dakka for medical advice right? right??", et cetera.
When I worked for what was basically a mom and pop version of Geek Squad, we found ASUS generally to be decent devices, but that was about 10 years ago.
With regard to the
OP: I prioritize the feel of the laptop over and beyond the power of it. It's a laptop. You basically either optimize for portability and comfort, or you optimize for power. And if you're optimizing for power, you don't want a laptop, you want a desktop.
So obviously, I optimize for portability, and so I usually look for something somewhat ultrabook-ish or Macbook-ish. Reason being is because if I'm looking for a laptop, it's probably because I want to take it places without feeling like I've got a boat anchor in my backpack. Secondarily, I always, ALWAYS,
ALWAYS find a store that has the laptop physically situated in it for me to pound on the keyboard for a few minutes at a time to see how it feels. I click around on the touch pad for a while. If it has the little nubby thing, I play with the little nubby thing. This is secondary to the size, but really they should be about equal. If it sucks to type on, and the touchpad sucks to mouse around on, and you need an external mouse and keyboard to use it comfortably, then it's not really a laptop.
Having that been said, I also know how to keep a computer clean, do a full wipe and reinstall every year or two, and don't generally do anything other than programming or work on the laptop, so I don't really need much more than an i3 for just about anything. Your mileage might vary. And from a personal point of view, I'm not entirely sure I'd spend more than maybe $500 max on any fragile electronic device for a 10 year old. I'm not even sure I'd spend half that. I don't have children though, so who knows.
As a final note,
WRT tablet+keyboard, I know a guy who used a iPad and a logitech keyboard for quite a while fairly comfortably. I have a Nexus 7 and a China special keyboard, and while they work, they fail the above pound test pretty hard. I say phones and tablets are for consuming, while computers are for producing. Having that been said, I know three programmers who have the Surface Pro, which is more like an actual computer, and they love the hell out of them, so that sounds like the exception to the general rule.