Consider getting your kid a touch screen laptop if you are still in the market for one. I wasn't a bug fan of metro until I got one and now I use it more and more.
I've been thinking about a surface, anyone have any anecdotes about how their kids responded to that? I selfishly want the Wacom stylus functionality for myself.
A friend's children (aged 6 and 8) use my Surface occasionally, mainly for the Fresh Paint drawing application. They love it, and have very few problems using it -- sometimes they misjudge the swipe gestures but they have learned how to recover in most cases. (They also enjoy ArtRage on the iPad, so it's not that Surface is the only thing they know.)
And how much extra would that cost?
I don't think it costs much extra. I have seen a decent touch screen laptop at around $500. Many lower than that. Find some here. http://www.edealpc.com/ Filter by touch screen.