You are solving the wrong problem. What you are doing, is searching for an environment for a person unfamiliar with computers. This should be a second step really.
The first step should be (I think) "what should I buy for 10 YEAR OLD".
First of all - I think that netbooks AND notebooks (from 7" to 20") for a child is a bad idea. Netbooks (7" to 10") is especially bad idea.
You should consider her eyesight - small, high dpi display very close to the eyes is bad.
Consider scoliosis probability - because keyboard is fixed right below the screen and can't disconnected (except 1-2 special rare big notebooks).
Consider RSI (repetitive strain injury) to hands, neck etc., hands especially. This can be caused by bad keyboard (all notebooks I think), screen keyboards (on extended use, like writing code, essays etc.), even bad mouse (cause hand position on the mouse is unnatural, it is a 90* turn from ideal position). Developed hand RSI is unbearably painful, considerably limits keyboard usage and heals very, very bad.
This is just what I would consider. Ask a medic and he'll tell you more.
tl;dr
No notebooks and probably tablets for 10 year old. Buy adjustable table, adjustable chair, classic desktop with some ergonomic keyboard and mouse (both with wrist support). Set up timed lockout on the PC, like 10 minutes every 1-2 hours. Lockout after 24:00 and lockout on total uptime per day. After that choose OS from your experience, it doesn't matter really (I think).
The RSI risk and your other ergonomic notes have nothing to do with someone's age.
I completely agree with 'icebraining' concerning your idea of computer-forced strictly timed lockouts: not a good idea.
Consider scoliosis probability [..]
Now you are just making plausibly sounding stuff up to support your position. No link between scoliosis and laptop use has ever been established and there is no reason to suppose a link, except for a naive idea about the bodily position during 'laptop use' and 'spine deformity'.
> What you are doing, is searching for an environment for a person unfamiliar with computers
Where did I say she is unfamiliar with computers? Her and her younger sister already use an almost dead family laptop for Skype, creating documents and playing games. They were figuring out how to search for Dora games before they could spell (use phonetics). They are far more proficient at Angry Birds than you will ever be and not too bad at Desktop Tower Defence. Homework essays are compiled via online research and includes lots of pictures and nice layout.
Human beings are not as fragile as your response implies.
Set up timed lockout on the PC, like 10 minutes every 1-2 hours
That would be more than enough to discourage me of ever becoming proficient at this. The "zone" applies when you're just learning too, and breaking it is extremely frustrating. Can you imagine closing the lid of the piano just as the kid is playing some difficult piece correctly for the first time?
There should be limits, but they should be soft and enforced by whoever is watching the child, who can presumably understand if (s)he's really excited or just bullshitting on Miniclip or IM.
1. No one stops you from keeping "zone" feeling during lockout, you can just drink something (what actually helps to think a lot is to drink regularly) or sit for a while with closed eyes thinking about problem, etc.
1a. I sincerely think that regular breaks actually help solving problems (at least in some cases).
2. Schools use timed breaks and in rare cases of interesting classes they do not discourage students to learn. Of course schools should be optimized more, I'm not arguing that.
3. Timed lockout is not target, invented just to prevent illness, it is also a method. Method to teach self discipline, even to begin teaching self discipline in some cases. No one will tell you how to optimize living when you'll grow up, that is why we read a lot of articles about people who burn out on a job.
Later it is insanely hard to go from super lazy, undisciplined student to focused worker.
Solving problems is what you do after you learn to code. A kid is still just poking and experimenting, and a hard lockout is, in my experience as a kid myself, a great way to kill that excitement.
I'm not saying you shouldn't have regular breaks, I'm saying a kid should have leeway to use e.g. half an hour more and then do a longer break, not feel a pressure to finish stuff in a hurry before it locks out.
Schools use timed breaks and in rare cases of interesting classes they do not discourage students to learn.
Obviously we have very different experiences.
3. Timed lockout is not target, invented just to prevent illness, it is also a method. Method to teach self discipline, even to begin teaching self discipline in some cases. No one will tell you how to optimize living when you'll grow up, that is why we read a lot of articles about people who burn out on a job.
First, I'm not opposed to lockouts. I'm opposed to inflexible, computer enforced lockouts.
Secondly, is there any evidence that timed lockouts actually help with self discipline?
tl;dr No notebooks and probably tablets for 10 year old. Buy adjustable table, adjustable chair, classic desktop with some ergonomic keyboard and mouse (both with wrist support). Set up timed lockout on the PC, like 10 minutes every 1-2 hours. Lockout after 24:00 and lockout on total uptime per day. After that choose OS from your experience, it doesn't matter really (I think).
I promise, she'll thank you 15 years later.