Looked at some spec o the variois side-by-sides but I think I'd still opt for a regular ole 4-wheeler. I like that my son could go wth me in a SxS though. Would need to trailer whatever lg machine I get anyways. What I did find interesting is that in clicking on your link above, I found that Polaris is marketing a youth Sxs now. A bit big for my 7 yo but maybe others will follow suit. Looks to be a new untapped market.
First and foremost on your new buggie - be safe!