Preface my background
I tutor elementary and junior high students one on one. My tablet of choice is the hp tc1100. I have a student with dysgraphsia (writing problems), who responded to the use of the tc1100 to aid in learning to write. The unit has xp and has the student experience pack- carrying flashcards and worksheets that can be done on the unit! Makes a great white board and so on. So my opinion is biased not just toward the tc1100, but toward ACTIVE DIGITIZERS for students in general.
You could always look at used units-
One of the reasons I chose the older hp tc1100 for a unit for my child was the fact that you don't have to change your handwriting style to use it. To me this is important for children. Now others might have different suggestions- I know John had a picture of a child and I'm not sure which unit the child was working with. In any case It is important to have an "Active Digitizer" if the child is going to write any kind of notes. This would mean that it would use a stylus! The touch models are attractive, but they are not designed for writing.
You might also look into getting a Franklin Covey Planplus older version for notebooks - the onboard journal is fine, but for organization of notes this is a better less confusing program for a child.
the problem with older units is the lack of battery life. If you get an older unit purchase a new battery for it.
If you are looking for new-- Fujitsu, and motion have active digitizer units!
Another key- not too big- the child is 12 a 14 inch screen to lug around will be hard to handle. I'd say smaller is better, but not too small because then the pages and scrolling become an issue.
My recommendation would be to stay within 9-12" screens.
Active Digitizer with Stylus
Planplus style software for notebook organization
fujitsu and motion newer units with active digitizer
screen size 9-12"
Questions to ask
What will my child use this for? Reading only? Handwriting and notes, drawing? Websurfing only . . .
This would determine the digitizer use whether active (use with stylus needed) or touch (capacitive and multi)
the usual questions about memory, and operating systems and such?
TC1000 tc1100 tc4200 and now a tc4400