Working in a Trek dealership I've sold my fair share of 820s. Their the bread and butter of what the shop sells and what people are looking for when they want an inexpensive bike shop quality bike. It's a steel frame and really basic sprung non adjustable fork. I think once your at that level of bikes it's apples to apples. I honestly like steel bikes more so then aluminum. I wish Trek would put the 820 back to a fully rigid mountain bike like it used to be and ditch the useless anchor of a suspension fork.
As far as kids bikes even working at a shop I'll tell people that kids bikes are kids bikes. It's just who puts them together. Buy a used kids bike that fits because they'll out grow it soon and their normally hard on bikes.
Can't comment on the Specialized and I can't stand them as a Company and the crap they pull.