I don't understand how you can think the XL is meant for children, especially when the reason many people upgrade to the XL (myself included) is because their adult hands cramp up on the tiny 3DS clearly designed with a kid's hands in mind.
And how can you call the XL unwieldy and the Vita perfectly portable in the same sentence? XL is roughly the same size as the Vita, and has the clamshell design that makes pocket carrying loads easier without having to worry about damaging sensitive analogs by cramming them against your pocket or getting dust in between them.
No offense, but I really doubt you've ever touched an XL.